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1.
Enhancement of oxygen mass transfer in stirred bioreactors using oxygen-vectors. 1. Simulated fermentation broths 总被引:4,自引:0,他引:4
Oxygen mass transfer represents the most important parameter involved in the design and operation of mixing-sparging equipment for bioreactors. It can be described and analyzed by means of the mass transfer coefficient, kLa. The kLa values are affected by many factors such as geometrical and operational characteristics of the vessels, media composition, type, concentration and microorganism morphology, and biocatalysts properties. The efficiency of oxygen transfer could be enhanced by adding oxygen-vectors in broths, such as hydrocarbons or fluorocarbons, without increasing the energy consumption for mixing or aeration. The experimental results obtained for simulated broths indicated a considerable increase of kLa in the presence of n-dodecane, and the existence of a certain value of n-dodecane concentration that corresponds to a maximum mass transfer rate of oxygen. The magnitude of the positive effect of n-dodecane depends both on the broths characteristics and operational conditions of the bioreactor.Notation d stirrer diameter, mm - d oxygen electrode diameter, mm - D bioreactor diameter, mm - h distance from the inferior stirrer to the bioreactor bottom, mm - H bioreactor height, mm - kLa oxygen mass transfer coefficient, s-1 - l impeller blade length, mm - I oxygen electrode immersed length, mm - P power consumption for mixing of non-aerated broths, W - Pa power consumption for mixing of aerated broths, W - (Pa/V) specific power input, W/m3 - s baffle width, mm - vS superficial air velocity, m/s - V volume of medium, m3 - w impeller blade height, mm - volumetric fraction of oxygen-vector - a apparent viscosity, Pa*s - density, kg/m3 相似文献
2.
The effect of phlorizin has been tested on hexose transport and hexose-induced changes of electrical potential (m) and conductance (g
m) across the plasmalemma of rhizoid and thallus cells of the aquatic liverwort Riccia fluitans. The decrease of m (depolarization) and g
m induced by 1 mM 3-oxymethyl-D-glucose (3-OMG) is substantially inhibited by simultaneous addition of 2 mM phlorizin, whereas no significant response was observed when phlorizin was added alone or several minutes after the sugar. Current-voltage data show that the 3-OMG-generated electrical inward current of 0.016 A m-2 drops to 0.010 A m-2 when phlorizin is present. Uptake as well as efflux of [14C]-3-OMG is strongly and reversibly inhibited by phlorizin between 0.2 and 5 mM. The results are consistent with our hypothesis that the hexose carrier has one binding site with competitive inhibition of glucose uptake by phlorizin (k
i=0.08 mM). The electrical data indicate that phlorizin affects an m step of the carrier transport cycle.Abbreviation 3-OMG
3-oxymethyl-D-glucose 相似文献
3.
A microsomal vesicle fraction (GV) markedly enriched by the Golgi marker enzyme latent inosine diphosphatase (IDPase) has been isolated from photoautotrophic suspension-cell protoplasts ofChenopodium rubrum L. Addition of ATP creates a substantial pH gradient across the GV membrane as measured by accumulation of acridine orange. The GV showed a density of 1.14 g·cm-3 by equilibrium density centrifugation on sucrose gradients. Coincidence of acridine-orange accumulation and IDPase activity was confirmed on Percoll gradients. Formation of the pH gradient half-saturates at 0.3 mM MgATP, peaks at pH 7, and is competitively inhibited by ADP (k
i0.1 mM), but not by Pi; it is hardly inhibited by orthovanadate, quickly dissipated by monensink
2=18 nM), nigericin (k
1/2=25 nM), and sluggishly by N-ethylmaleimide (k
1/235 M). Inhibition by KNO3 (k
1/26.7 mM) is incomplete (60%). Uridine 5-diphosphate (UDP)-glucose, UDP-galactose, but not UDP-mannose and the pertinent sugars, dissipate the ATP-generated pH gradient (k
1/210–20 mM UDP-glucose; optimum pH at 7.8). This UDP-glucose activity is accompanied by release of Pi, but not of glucose or sucrose. UDP-glucoseinduced Pi release from the GV saturates (k
1/2=1 mM UDP-glucose; optimum pH at 7) and is completely inhibited by the anion-channel blocker 4,4-diisothiocyano-2,2-stilbene disulfonic acid (DIDS;k
1/2=140 M). The GV incorporates UDP-[U-14C]glucose into an acid-labile, alkaline-stable macromolecular compound; this process is like-wise inhibited by DIDS. We propose a model including, inter alia, a UDP-glucose/uridine-5-monophosphate translocator and a phosphate-permeable anion channel to operate in Golgi vesicles ofChenopodium rubrum.Abbreviations AO
acridine orange
- DIDS
4,4-diisothiocyano-2,2-stilbene disulfonic acid
- FCCP
carbonyl cyanidep-trifluoromethyoxyphenyl hydrazone
- GV
Golgi-vesicle-enriched microsomal fraction
- IDPase
mosine diphosphatase 相似文献
4.
The spectral control of hypocotyl elongation in light-grown Chenopodium rubrum L. seedlings has been studied. The results showed that although the seedlings responded to changes in the quantity of combined red and far-red radiation, they were also very sensitive to changes in the quantity of blue radiation reaching the plant. Altering the proportion of red: far-red radiation in broad waveband white light caused marked differences in hypocotyl extension. Comparison of the responses of green and chlorophyll-free seedlings indicated no qualitative difference in the response to any of the light sources used, although photosynthetically incompetent plants were more sensitive to all wavelengths. Blue light was found to act primarily of a photoreceptor which is different from phytochrome. It is concluded that hypocotyl extension rate in vegetation shade is photoregulated by the quantity of blue light and the proportion of red: far-red radiation. In neutral shade, such as that caused by stones or overlying soil, hypocotyl extension appears to be regulated primarily by the quantity of light in the blue waveband and secondarily by the quantity of light in the red and far-red wavebands.Abbreviations B
blue
- FR
far-red
-
k
1, k
2
rate constants for photoconverison of Pr to Pfr and Pfr to Pr, respective
-
k
1/k
1
+k
2=
phytochrome photoequilibrium
-
k
1
+k
2=
phytochrome cycling rate
- Pr=R
absorbing form of phytochrome
- Pfr=FR
absorbing form of phytochrome
- Ptot
Pr+Pfr
- PAR
photosynthetically active radiation = 400–700 nm
- R
red
- WL
white light 相似文献
5.
Substrate specificity and product inhibition of different forms of fructokinases and hexokinases in developing potato tubers 总被引:10,自引:0,他引:10
The substrate dependence and product inhibition of three different fructokinases and three different hexokinases from growing potato (Solanum tuberosum L.) tubers was investigated. The tubers contained three specific fructokinases (FK1, FK2, FK3) which had a high affinity for fructose K
m=64, 90 and 100 (M) and effectively no activity with glucose or other hexose sugars. The affinity for ATP (K
m=26, 25 and 240 M) was at least tenfold higher than for other nucleoside triphosphates. All three fructokinases showed product inhibition by high fructose (K
i=5.7, 6.0 and 21 mM) and were also inhibited by ADP competitively to ATP. Sensitivity to ADP was increased in the presence of high fructose, or fructose-6-phosphate. In certain conditions, the K
i (ADP) was about threefold below the K
m (ATP). All three fructokinase were also inhibited by fructose-6-phosphate acting non-competitively to fructose (K
i=1.3 mM for FK2). FK1 and FK2 showed very similar kinetic properties whereas FK3, which is only present at low activities in the tuber but high activities in the leaf, had a generally lower affinity for ATP, and lower sensitivity to inhibition by ADP and fructose. The tuber also contained three hexokinases (HK1, HK2, HK3) which had a high affinity for glucose (K
m=41, 130 and 35 M) and mannose but a poor affinity for fructose (K
m=11, 22 and 9 mM). All three hexokinases had a tenfold higher affinity for ATP (K
m=90, 280 and 560 M) than for other nucleoside triphosphates. HK1 and HK2 were both inhibited by ADP (K
i=40 and 108 M) acting competitively to ATP. HK1, but not HK2, was inhibited by glucose-6-phosphate, which acted non-competitively to glucose (K
i=4.1 mM). HK1 and HK2 differed, in that HK1 had a narrower pH optimum, a higher affinity for its substrate, and showed inhibition by glucose-6-phosphate. The relevance of these properties for the regulation of hexose metabolism in vivo is discussed.Abbreviations FK
fructokinase
- Fru6P
fructose-6-phosphate
- Glc6P
glucose-6-phosphate
- HK
hexokinase
- NTP
nucleoside triphosphate
- Pi
inorganic phosphate
- UDPGlc
uridine-5-diphosphoglucose
This work was supported by the Deutsche Froschungsgemeinschaft (SFB 137). We are grateful to Professor E. Beck (Lehrstuhl für Pflanzenphysiologie, Universität Bayreuth, FRG) for providing laboratory facilities. 相似文献
6.
Cosme R. Martínez André M. Netto Márcia V.B. Figueiredo Benildo S. Cavada José L. Lima-Filho 《World journal of microbiology & biotechnology》2005,21(1):75-82
Lectins from Canavalia brasiliensis (CnBr), Cratylia floribunda (CFL), Vatairea macrocarpa (VML) and Phaseolus vulgaris (PHA) aggregate Rhizobiumbacteria. The relationship between specific sedimentation rate, (based on bacterial dry biomass) of bacterial aggregates and lectin concentrations was hyperbolic and showed bacterial surface affinity by lectins. R. tropici (Rt), R. leguminosarum bv. phaseoli (Rlp) and R. etli (Re) surfaces showed predominantly receptors of galactosidic nature. The Rt surfaces showed very high affinities (k s = ±8.6 × 10–8 ag lectin protein ml–1) by Gal-specific lectins (PHA and VML), and very low affinities (ks=± 4.9 × 10–6) by Glc-specific lectins (CnBr and CFL). The Rlp surface had intermediate affinities by lectins. The Re surface showed high affinities by PHA (ks= ±1.26 × 10–8) and intermediate affinities by VML, CnBr and CFL. The relationship between sedimentation specific (based on lectin weight) and bacterial density was a sigmoid and showed lectin affinity by Rt surfaces. The bacterial sedimentation showed positive cooperative binding of lectins. The Vmax induced by Glc-specific lectins was ±20 of that produced by Gal-specific lectins. The PHA affinity (ks= 1.19 mg dry biomass ml–1) was larger than VML (ks = 1.23). The Glc-specific lectin affinities were smaller than those of Gal-specific. The apparent binding site number of lectins (napp) was: 2.7-PHA; 2.2-VML; 3.2-CFL and 3.2-CnBr. The dissociation constant, ks, of lectin-binding kinetics decreased with sugar-hapten treatment (10 M). The napp decreased in PHA and CFL, increasing in VML + sugar-hapten treatment. This study showed that there is a difference in Rhizobium surfaces for lectin binding. 相似文献
7.
The molar growth yield (Y
m) of Bacteroides amylophilus strain WP91 on maltose was 68±2 g/mol when determined from batch cultures at the peaks of maximal growth. Continued incubation led to considerable cell lysis. When calculated from batch cultures in exponential phase (specific growth rate, =0.57 h-1) Y
m was 101 g/mol. The maximum value of Y
m in maltose-limited chemostat cultures at the maximum dilution rate (D) attainable (D==0.39 h-1) was about 79 g/mol. Ammonia-Fmited chemostat cultures metabolized maltose with a much reduced efficiency and this was associated with a difference in morphology and chemical composition of the cells. The theoretical maximum molar growth yields (Y
m
max
) were 55 and 114 g/mol for ammonia- and maltose-limited growth respectively. However, if account was taken of extracellular nitrogen-containing material in ammonia-limited cultures, Y
m
max
became 60. The maintenance coefficient (m
s), estimated from the lines relating the specific rate of maltose consumption (q
m) and D (where m
s=q
m at D=0), was 7.4±0.6×10-4 mol maltose/g x h for both nutrient limitations. A difference in maintenance energy demand, independent of growth-rate, could not account, therefore, for the observed differences in Y
m between ammonia- and maltose-limited growth. 相似文献
8.
K. Hager A. Hazama H. M. Kwon D. D. F. Loo J. S. Handler E. M. Wright 《The Journal of membrane biology》1995,143(2):103-113
The two-microelectrode voltage clamp technique was used to examine the kinetics and substrate specificity of the cloned renal Na+/myo-inositol cotransporter (SMIT) expressed in Xenopus oocytes. The steady-state myo-inositol-induced current was measured as a function of the applied membrane potential (V
m
), the external myo-inositol concentration and the external Na+ concentration, yielding the kinetic parameters: K
0.5
MI
, K
0.5
Na
, and the Hill coefficient n. At 100 mM NaCl, K
0.5
MI
was about 50 m and was independent of V
m
. At 0.5 mm
myo-inositol, K
0.5
Na
ranged from 76 mm at V
m
=–50 mV to 40 mm at V
m
=–150 mV. n was voltage independent with a value of 1.9±0.2, suggesting that two Na+ ions are transported per molecule of myo-inositol. Phlorizin was an inhibitor with a voltage-dependent apparent K
I
of 64 m at V
m
=–50 mV and 130 m at V
m
= –150 mV. To examine sugar specificity, sugar-induced steady-state currents (at V
m
=–150 mV) were recorded for a series of sugars, each at an external concentration of 50 mm. The substrate selectivity series was myo-inositol, scyllo-inositol > l-fucose > l-xylose > l-glucose, d-glucose, -methyl-d-glucopyranoside > d-galactose, d-fucose, 3-O-methyl-d-glucose, 2-deoxy-d-glucose > d-xylose. For comparison, oocytes were injected with cRNA for the rabbit intestinal Na+/glucose cotransporter (SGLT1) and sugar-induced steady-state currents (at V
m
=–150 mV) were measured. For oocytes expressing SGLT1, the sugar selectivity was: d-glucose, -methyl-d-glucopyranoside, d-galactose, d-fucose, 3-O-methyl-d-glucose > d-xylose, l-xylose, 2-deoxy-d-glucose > myo-inositol, l-glucose, l-fucose. The ability of SMIT to transport glucose and SGLT1 to transport myo-inositol was independently confirmed by monitoring the Na+-dependent uptake of 3H-d-glucose and 3H-myo-inositol, respectively. In common with SGLT1, SMIT gave a relaxation current in the presence of 100 mm Na+ that was abolished by phlorizin (0.5 mm). This transient current decayed with a voltage-sensitive time constant between 10 and 14 msec. The presteady-state current is apparently due to the reorientation of the cotransporter protein in the membrane in response to a change in V
m
. The kinetics of SMIT is accounted for by an ordered six-state nonrapid equilibrium model.
Present address: W.M. Keck Biotechnology Resource Laboratory, Boyer Center for Molecular Medicine, Rm, 305A, Yale University, 295 Congress Ave., New Haven, Connecticut 06536-0812
Present address: National Institute for Physiological Sciences, Department of Cell Physiology, Okazaka, 444, JapanContributed equally to this workWe thank John Welborn for the HPLC analysis of the sugar substrates. This work was supported by grants from the National Institutes of Health DK19567, DK42479 and NS25554. 相似文献
9.
V. V. Likhareva B. V. Vas'kovskii N. E. Shepel' S. K. Garanin A. G. Mikhailova L. D. Rumsh 《Russian Journal of Bioorganic Chemistry》2003,29(2):112-117
Enteropeptidase (enterokinase, EC 3.4.21.9) hydrolyzes peptide bonds formed by carboxyl groups of Lys or Arg residue if less than four negatively charged amino acid residues are in positions P
2–P
5 of its substrate. We determined the kinetic parameters of three substrates of this type: human angiotensin II (AT) (DR VYIHPF) and the Hb(2–8) (LTAEEK A) and Hb(1–9) (MLTAEEK AA) peptides of the cattle hemoglobin -chain. The K
m values for all the substrates (10–3 M) were one order of magnitude higher than those of the typical synthetic substrates of enteropeptidase or chimeric proteins with the –DDDDK– full-size linker (K
m 10–4 M). The k
cat values for AT and Hb(2–8) were also close and low (30 min–1). The general hydrolysis efficiency of such substrates is no more than 1% of the corresponding value for the typical peptide and protein substrates of the enteropeptidase. However, the elongation of Hb(2–8) peptide by one amino acid residue from both its N- and C-termini results in a dramatic increase in the catalytic efficiency of the hydrolysis: the k
cat value for Hb(1–9) is 1510 min–1, which means that it is hydrolyzed only three times less effective than the chimeric protein with the full-size linker. 相似文献
10.
Solute mobilities of 28 compounds in isolated cuticular membranes (CM) from Capsicum annuum L. fruit, Citrus aurantium L. and Pyrus communis L. leaves were studied using unilateral desorption from the outer surface. First-order rate constants of desorption (k*), which are directly proportional to the diffusion coefficient in the waxy outer limiting skins of cuticles were measured. When log k* was plotted vs. molar volumes of test compounds linear graphs were obtained. The y-intercepts of these graphs (k*) represent the mobility of a hypothetical molecule having zero molar volume and the slopes of the graphs () represent the size selectivity of the barrier and are related to the free volume available for diffusion. Thus, solute mobilities in cuticles are composed of two independent terms which are subtractive. If k* and are known, k* can be estimated for any solute from its molar volume (Vx) using the equation log k*=log k* –Vx. These parameters were used to analyse the effects of plant species, extraction of cuticular waxes and molecular structure of solutes on solute mobilities in plant cuticles. For aliphatic solutes, k* was a factor of 10 smaller than for cyclic compounds, while was 0.011 and 0.012, respectively. The k*-values for CM of the three species were very similar, but was higher for bitter-orange CM (0.012) than for those of pepper fruits and pear leaves (0.009). This has the consequence that differences in solute mobilities (k*) among cuticles from different plan species increase with increasing molar volumes of solutes. Our data and our analysis provide evidence that constituents of cuticular waxes are mobile, at least in the solid amorphous wax fraction, but mobility decreases rapidly with increasing molar volume. For instance, if amounts to 0.01, mobilities of wax monomers decrease by a factor of 10 for every increase in molar volume of 100 cm3 · mol–1. Thus, hexadecanoic acid is quite mobile in the amorphous wax fraction of Citrus (k*=1.5×10–6·s–1), but for dotriacontane having twice the molar volume, k* was only 2.5×10–9·s–1, which is almost three orders of magnitude smaller. Wax esters have even higher molar volumes and their mobilities will be even smaller (about 4×10–12·s–1 for a C48-ester). Since low chain mobilities are a prerequisite for low mobilities and permeabilities, the selective advantage of high-molecular-weight wax monomers in plant cuticular waxes becomes obvious. Extracting cuticular waxes from pear leaf CM increased solute mobilities by a factor of 182, but it had no effect on size selectivity. We interpret this result as evidence to the effect that cuticular waxes reduce mobility by increasing tortuosity of the diffusion path, rather than by decreasing the mean free path of diffusional jumps and jump frequencies of diffusants.Abbreviations CM
cuticular membrane(s)
- 2,4-D
2,4-dichloro-phenoxyacetic acid
- LAB
lactic acid buffer
- MX
polymer matrix membranes
- UDOS
unilateral desorption from the outer surface 相似文献
11.
Gerhard Sandmann 《Photosynthesis research》1987,11(1):37-44
The endogenous plastocyanin (PC) concentrations of Dunaliella cultures were varied from 0.3 to 3.1 molecules per pigment 700 (P700) by decreasing the Cu+ supply of the nutrient. With these cultures the amount of PC which is sufficient for maximum photosynthesis in intact cells was determined to be about 1 to 1.5 PC/P700. Chloroplasts were also prepared from these cells and were employed in enzyme kinetic measurements of the PSI reaction from ascorbate reduced diaminodurene (DAD) to methylviologen/O2. The k
m value for DAD in this reaction was 106 M. A decrease of the endogenous PC concentration caused no change of the k
m value but affected the V
max in the DAD-dependent reaction. A similar interference of the PC concentration on the maximum reaction rate could also be observed when the light intensity was varied. 相似文献
12.
Photoinhibition of photosynthesis was induced in intact kiwifruit (Actinidia deliciosa (A. Chev.) C. F. Liang et A. R. Ferguson) leaves grown at two photon flux densities (PFDs) of 700 and 1300 mol·m-2·s-1 in a controlled environment, by exposing the leaves to PFD between 1000 and 2000 mol·m-2·s-1 at temperatures between 10 and 25°C; recovery from photoinhibition was followed at the same range of temperatures and at a PFD between 0 and 500 mol·m-2·s-1. In either case the time-courses of photoinhibition and recovery were followed by measuring chlorophyll fluorescence at 692 nm and 77K and by measuring the photon yield of photosynthetic O2 evolution. The initial rate of photoinhibition was lower in the high-light-grown plants but the long-term extent of photoinhibition was not different from that in low-light-grown plants. The rate constants for recovery after photoinhibition for the plants grown at 700 and 1300 mol·m-2·s-1 or for those grown in shade were similar, indicating that differences between sun and shade leaves in their susceptibility to photoinhibition could not be accounted for by differences in capacity for recovery during photoinhibition. Recovery following photoinhibition was increasingly suppressed by an increasing PFD above 20 mol·m-2·s-1, indicating that recovery in photoinhibitory conditions would, in any case, be very slow. Differences in photosynthetic capacity and in the capacity for dissipation of non-radiative energy seemed more likely to contribute to differences in susceptibility to photoinhibition between sun and shade leaves of kiwifruit.Abbreviations and symbols
F
o
, F
m
, F
v
instantaneous, maximum, variable fluorescence
-
F
v
/F
m
fluorescence ratio
-
F
i
=F
v
at t=0
-
F
F
v
at t=
-
K
D
rate constant for photochemistry
-
k(F
p
)
first-order rate constant for photoinhibition
-
k(F
r
)
first-order rate constant for recovery
- PFD
photon flux density
- PSII
photosystem II
-
i
photon yield of O2 evolution (incident light) 相似文献
13.
Desulfobacter postgatei is an acetate-oxidizing, sulfate-reducing bacterium that metabolizes acetate via the citric acid cycle. The organism has been reported to contain a si-citrate synthase (EC 4.1.3.7) which is activated by AMP and inorganic phosphate. It is show now, that the enzyme mediating citrate formation is an ATP-citrate lyase (EC 4.1.3.8) rather than a citrate synthase. Cell extracts (160,000xg supernatant) catalyzed the conversion of oxaloacetate (apparent K
m=0.2 mM), acetyl-CoA (app. K
m=0.1 mM), ADP (app. K
m=0.06 mM) and phosphate (app. K
m=0.7 mM) to citrate, CoA and ATP with a specific activity of 0.3 mol·min-1·mg-1 protein. Per mol citrate formed 1 mol of ATP was generated. Cleavage of citrate (app. K
m=0.05 mM; V
max=1.2 mol · min-1 · mg-1 protein) was dependent on ATP (app. K
m=0.4 mM) and CoA (app. K
m=0.05 mM) and yielded oxaloacetate, acetyl-CoA, ADP, and phosphate as products in a stoichiometry of citrate:CoA:oxaloacetate:ADP=1:1:1:1. The use of an ATP-citrate lyase in the citric acid cycle enables D. postgatei to couple the oxidation of acetate to 2 CO2 with the net synthesis of ATP via substrate level phosphorylation. 相似文献
14.
The activity of purified N
5,N
10-methenyltetrahydromethanopterin cyclohydrolase from Methanopyrus kandleri was found to increase up to 200-fold when potassium phosphate was added in high concentrations (1.5 M) to the assay. A 200-fold stimulation was also observed with sodium phosphate (1 M) and sodium sulfate (1 M) whereas stimulation by potassium sulfate (0.8 M), ammonium sulfate (1.5 M), potassium chloride (2.5 M), and sodium chloride (2 M) was maximal 100-fold. A detailed kinetic analysis of the effect of potassium phosphate revealed that this salt exerted its stimulatory effect by decreasing the K
m for N
5,N
10-methenyltetrahydromethanopterin from 2 mM to 40 M and by increasing the V
max from 2000 U/mg (kcat=1385 s-1) to 13300 U/mg (kcat=9200 s-1). Besides increasing the catalytic efficiency (kcat/K
m) salts were found to protect the cyclohydrolase from heat inactivation. For maximal thermostability much lower concentrations (0.1 M) of salts were required than for maximal activity.Abbreviations H4MPT
tetrahydromethanopterin
-
N
5,N
10-methenyl-H4MPT
- CHO-H4MPT
N
5-formyl-H4-MPT
- CH2=H4MPT
N
5,N
10-methylene-H4MPT
- CH3–H4-MPT
N
5-methyl-H4MPT
- MOPS
-N-morpholinopropane sulfonic acid
- TRICINE
N-[Tris(hydroxymethyl)-methyl]glycine
- 1 U =
1 mol/min 相似文献
15.
Adam M. Gilmore Theodore L. Hazlett Peter G. Debrunner Govindjee 《Photosynthesis research》1996,48(1-2):171-187
Photosystem II (PS II) chlorophyll (Chl) a fluorescence lifetimes were measured in thylakoids and leaves of barley wild-type and chlorina f104 and f2 mutants to determine the effects of the PS II Chl a+b antenna size on the deexcitation of absorbed light energy. These barley chlorina mutants have drastically reduced levels of PS II light-harvesting Chls and pigment-proteins when compared to wild-type plants. However, the mutant and wild-type PS II Chl a fluorescence lifetimes and intensity parameters were remarkably similar and thus independent of the PS II light-harvesting antenna size for both maximal (at minimum Chl fluorescence level, Fo) and minimal rates of PS II photochemistry (at maximum Chl fluorescence level, Fm). Further, the fluorescence lifetimes and intensity parameters, as affected by the trans-thylakoid membrane pH gradient (pH) and the carotenoid pigments of the xanthophyll cycle, were also similar and independent of the antenna size differences. In the presence of a pH, the xanthophyll cycle-dependent processes increased the fractional intensity of a Chl a fluorescence lifetime distribution centered around 0.4–0.5 ns, at the expense of a 1.6 ns lifetime distribution (see Gilmore et al. (1995) Proc Natl Acad Sci USA 92: 2273–2277). When the zeaxanthin and antheraxanthin concentrations were measured relative to the number of PS II reaction center units, the ratios of fluorescence quenching to [xanthophyll] were similar between the wild-type and chlorina f104. However, the chlorina f104, compared to the wild-type, required around 2.5 times higher concentrations of these xanthophylls relative to Chl a+b to obtain the same levels of xanthophyll cycle-dependent fluorescence quenching. We thus suggest that, at a constant pH, the fraction of the short lifetime distribution is determined by the concentration and thus binding frequency of the xanthophylls in the PS II inner antenna. The pH also affected both the widths and centers of the lifetime distributions independent of the xanthophyll cycle. We suggest that the combined effects of the xanthophyll cycle and pH cause major conformational changes in the pigment-protein complexes of the PS II inner or core antennae that switch a normal PS II unit to an increased rate constant of heat dissipation. We discuss a model of the PS II photochemical apparatus where PS II photochemistry and xanthophyll cycle-dependent energy dissipation are independent of the Peripheral antenna size.Abbreviations Ax
antheraxanthin
- BSA
bovine serum albumin
- cx
lifetime center of fluorescence decay component x
- CP
chlorophyll binding protein of PS II inner antenna
- DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- DTT
dithiothreitol
- fx
fractional intensity of fluorescence lifetime component x
- Fm, Fm
maximal PS II Chl a fluorescence intensity with all QA reduced in the absence, presence of thylakoid membrane energization
- Fo
minimal PS II Chl a fluorescence intensity with all QA oxidized
- Fv=Fm–Fo
variable level of PS II Chl a fluorescence
- HPLC
high performance liquid chromatography
- kA
rate constant of all combined energy dissipation pathways in PS II except photochemistry and fluorescence
- kF
rate constant of PS II Chl a fluorescence
- LHCIIb
main light harvesting pigment-protein complex (of PS II)
- Npig
mols Chl a+b per PS II
- NPQ=(Fm/Fm–1)
nonphotochemical quenching of PS II Chl a fluorescence
- PAM
pulse-amplitude modulation fluorometer
- PFD
photon-flux density, mols photons m–2 s–1
- PS II
Photosystem II
- P680
special-pair Chls of PS II reaction center
- QA
primary quinone electron acceptor of PS II
- Vx
violaxanthin
- wx
width at half maximum of Lorentzian fluorescence lifetime distribution x
- Zx
zeaxanthin
- pH
trans-thylakoid proton gradient
- % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXafv3ySLgzGmvETj2BSbqef0uAJj3BZ9Mz0bYu% H52CGmvzYLMzaerbd9wDYLwzYbItLDharqqr1ngBPrgifHhDYfgasa% acOqpw0xe9v8qqaqFD0xXdHaVhbbf9v8qqaqFr0xc9pk0xbba9q8Wq% Ffea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qqQ8frFve9Fve9Ff0dme% GabaqaaiGacaGaamqadaabaeaafiaakeaacqGH8aapcqaHepaDcqGH% +aGpdaWgaaWcbaGaamOraiaad2gaaeqaaaaa!4989!\[< \tau > _{Fm}\],% MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXafv3ySLgzGmvETj2BSbqef0uAJj3BZ9Mz0bYu% H52CGmvzYLMzaerbd9wDYLwzYbItLDharqqr1ngBPrgifHhDYfgasa% acOqpw0xe9v8qqaqFD0xXdHaVhbbf9v8qqaqFr0xc9pk0xbba9q8Wq% Ffea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qqQ8frFve9Fve9Ff0dme% GabaqaaiGacaGaamqadaabaeaafiaakeaacqGH8aapcqaHepaDcqGH% +aGpdaWgaaWcbaGaamOraiaad+gaaeqaaOGaeyypa0Zaaabqaeaaca% WGMbWaaSbaaSqaaiaadIhaaeqaaOGaam4yamaaBaaaleaacaWG4baa% beaaaeqabeqdcqGHris5aaaa!50D3!\[< \tau > _{Fo} = \sum {f_x c_x }\]
average lifetime of Chl a fluorescence calculated from a multi-exponential model under Fm, Fo conditions 相似文献
16.
Decomposition of four macrophytes in wetland sediments: Organic matter and nutrient decay and associated benthic processes 总被引:3,自引:0,他引:3
Decomposition rates of Phragmites australis, Carex riparia, Nuphar luteum and Salvinia natans and benthic processes were measured from December 2003 to December 2004 in a shallow wetland (Paludi di Ostiglia, Northern Italy) by means of litter bags and intact cores incubations. Decay rate was highest for N. luteum (k = 0.0152 d−1), intermediate for S. natans (k = 0.0041 d−1) and similar for P. australis (k = 0.0027 d−1) and C. riparia (k = 0.0028 d−1).Benthic metabolism followed a seasonal pattern with summer peaks of O2 demand and TCO2, CH4 and NH4+ efflux whilst soluble reactive phosphorus (SRP) fluxes were negligible also under hypoxic conditions, indicating that P was mainly retained by sediment. The initial C:P ratio was similar in N. luteum and S. natans (170) and significantly lower than that of P. australis and C. riparia (360). During the detritus decay P was progressively lost by N. luteum and S. natans tissues, whereas, after an initial leaching, it was probably re-used during the microbial decomposition of the more refractory P. australis and C. riparia detritus. Nuphar luteum, P. australis and S. natans had comparable initial C:N mass ratio (15), significantly lower than that of C. riparia (26). The C:N ratio was rather constant for N. luteum (12.9 ± 1.5) and S. natans (14.6 ± 0.9), decreased slightly to below 20 for C. riparia and increased up to 30 for P. australis. Overall, differences among species were likely due to the recalcitrance of decomposing detritus, whilst process rates were controlled by limitation of microbial processes by nutrients and electron acceptor availability. 相似文献
17.
Four fluorescence parameters [Fv/Fm = the intrinsic efficiency of energy conversion via photosystem 2 (PS2); Fv/Fm= the efficiency of energy conversion via PS2 in the light; P = fraction of absorbed radiant energy utilized for photosynthesis; and D = fraction of absorbed radiant energy dissipated as heat] were measured on leaves of seven species of succulents having epidermal windows. While the function of leaf windows has reportedly been to increase absorption of radiant energy and, hence, the rate of photosynthesis in these species, recent evidence indicates that this translucent portion of epidermal tissue, lacking chlorophyll, may also result in photoinhibition in these species, especially for those with growth habits aboveground. Species with aboveground and belowground growth habits were compared with their leaf windows covered with reflective tape and with windows unobstructed. Results showed no increase in photoinhibition for these species resulting from the radiant energy penetrating the window tissue. Although the efficiency of the photosynthetic mechanism was not significantly influenced by the additional radiant energy provided by the window for individual species, there were significant differences in the efficiencies of radiant energy capture (Fv/Fm) and utilization (P) between the two growth habits. Species with an aboveground growth habit were less efficient in radiant energy utilization compared with the species having a belowground growth habit. 相似文献
18.
Jeffries V. E. Sastry G. R. K. 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1981,60(5):303-311
Summary The pallida gene of Antirrhinum majus governs anthocyanin production. The nature of the mutability displayed by its unstable allele pal-rec was dramatically altered following crosses between two pal-rec pal-rec lines with certain separately maintained lines. In both cases a minority of progeny in F1 or F2 revealed unprecedented infrequent mutability termed Low mutability. These Low plants and their sibs showed many areas of contrasting mutability superimposed on their initial mutability level. This frequent shifting and Low mutability persisted through several generations of offspring obtained by both selfing and crossing to a non-mutable tester line. Evidence is presented to suggest a hypothesis that the two features of altered mutability are two aspects of the same phenomenon caused by joint action of two independent factors J and k, one contributed by each parental line at the outcross.A separate gene, eosinea, governs anthocyanin type, eos eos plants having pelargonin in place of wild-type magenta cyanin. In addition to the previously known simple depression of pal-rec to Pal mutation frequency in eos eos plants, eos also influences the action of J and k when heterozygous (i.e. Eos eos), thus contributing a basal and a third tier of control influencing mutability of pal-rec.Three levels of control are thus identified, the middle tier being governed by the partnership of J and k producing not a simple change but a complex mutability of mutability. 相似文献
19.
Yoon HG Yang SW Kim HY Kim HK Shin DH Hong BS Cho HY 《Journal of Protein Chemistry》2000,19(7):621-630
Bacterial chitosanases share weak amino acid sequence similarities at certain regions of each enzyme. These regions have been assumed to be important for catalytic activities of the enzyme. To verify this assumption, the functional importance of the conserved region in a novel thermostable chitosanase (TCH-2) from Bacillus coagulans CK108 was investigated. Each of the conserved amino acid residues (Leu64, Glu80, Glu94, Asp98, and Gly108) was changed to aspartate and glutamine or asparagine and glutamate by site-directed mutagenesis, respectively. Kinetic parameters for colloidal chitosan hydrolysis were determined with wild-type and 10 mutant chitosanases. The Leu64 Arg and Leu64 Gln mutations were essentially inactive and kinetic parameters such as V
max and k
cat were approximately 1/107 of those of the wild-type enzyme. The Asp98 Asn mutation did not affect the K
m value significantly, but decreased k
cat to 15% of that of wild-type chitosanase. On the other hand, the Asp98 srarr; Glu mutation affected neither K
m nor k
cat. The observation that approximately 15% of activity remained after the substitution of Asp98 by Asn indicated that the carboxyl side chain of Asp98 is not absolutely required for catalytic activity. These results indicate that the Leu64 residue is directly involved in the catalytic activity of TCH-2. 相似文献
20.
Summary The voltage dependence for outward-going current of the Ca-activated K+ conductance (g
k (Ca)) of the human red cell membrane has been examined over a wide range of membrane potentials (V
m) at constant values of [K+]ex, [K+]c and pHc, the intact cells being preloaded to different concentrations of ionized calcium. Outward-current conductances were calculated from initial net effluxes of K+ and the corresponding (V
m-Ek) values. The basic conductance, defined as the outward-current coductance at (V
m-Ek) 20 mV and [K+]ex 3mM (B. Vestergaard-Bogind, P. Stampe and P. Christophersen,J. Membrane Biol.
95:121–130, 1987) was found to be a function of cellular ionized Ca. At all degrees of Ca activationg
K(Ca) was an apparently linear function of voltage (V
m range –40 to +70 mV), the absolute level as well as the slope decreasing with decreasing activation. In a simple two-state model the constant voltage dependence can, at the different degrees of Ca activation, be accounted for by a Boltzmann-type equilibrium function with an equivalent valence of 0.4, assuming chemical equilibrium atV
m=0 mV. Alternatively, the phenomenon might be explained by a voltage-dependent block of the outward current by an intracellular ion. Superimposed upon the basic conductance is the apparently independent inward-rectifying steep voltage function with an equivalent valence of 5 and chemical equilibrium at the givenE
K value.Abbreviations CCCP
carbonyl cyanidem-chlorophenylhydrazone
- DIDS
4,4-diisothiocyanostilbene-2,2-disul 相似文献