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1.
C. Xu S. M. D. Rogers C. Goldstein J. M. Widholm Govindjee 《Photosynthesis research》1989,21(2):93-106
We report here the first measurements on chlorophyll (Chl) a fluorescence characteristics of photoautotrophic soybean cells (cell lines SB-P and SBI-P). The cell fluorescence is free from severe distortion problems encountered in higher plant leaves. Chl a fluorescence spectra at 77 K show, after correction for the spectral sensitivity of the photomultiplier and the emission monochromator, peaks at 688, 696 and 745 nm, representing antenna systems of photosystem II-CP43 and CP47, and photosystem I, respectively. Calculations, based on the complementary area over the Chl a fluorescence induction curve, indicated a ratio of 6 of the mobile plastoquinone (including QB) to the primary stable electron acceptor, the bound plastoquinone QA. A ratio of one between the secondary stable electron acceptor, bound plastoquinone QB, and its reduced form QB
- was obtained by using a double flash technique. Owing to this ratio, the flash number dependence of the Chl a fluorescence showed a distinct period of four, implying a close relationship to the S state of the oxygen evolution mechanism. Analysis of the QA
- reoxidation kinetics showed (1) the halftime of each of the major decay components ( 300 s fast and 30 ms slow) increases with the increase of diuron and atrazine concentrations; and (2) the amplitudes of the fast and the slow components change in a complementary fashion, the fast component disappearing at high concentrations of the inhibitors. This implies that the inhibitors used are able to totally displace QB. In intact soybean cells, the relative amplitude of the 30 ms to 300 s component is higher (40:60) than that in spinach chloroplasts (30:70), implying a larger contribution of the centers with unbound QB. SB-P and SBI-P soybean cells display a slightly different sensitivity of QA
- decay to inhibitors.Abbreviations CA
complementary area over fluorescence induction curve
- Chl
chlorophyll, diuron
- DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
-
F
m
maximum chlorophyll a fluorescence
-
F
0
minimum chlorophyll a fluorescence
-
F
v =
F
t-F0
- where F
v =
variable chlorophyll a fluorescence
- and Ft =
chlorophyll a fluorescence at time t
- PS II
photosystem II
- Q
a
primary (plastoquinone) electron acceptor of PS II
- Q
b
secondary (plastoquinone) electron acceptor of PS II
- t50
the time at which the concentration of reduced Q
a
is 50% of that at its maximum value 相似文献
2.
A. J. Racher J. L. Moreira P. M. Alves M. Wirth U. H. Weidle H. Hauser M. J. T. Carrondo J. B. Griffiths 《Applied microbiology and biotechnology》1994,40(6):851-856
The growth and productivity of an Sp2/0 cell line, F3b10, expressing a recombinant antibody (rAb) and BHK21 cells expressing either the same rAb from the same plasmids (BHK.IgG) or secreted alkaline phosphatase (SEAP) (BHK.SEAP) were investigated. The F3b10 line was grown as a single cell suspension. The BHK lines were grown either as suspended natural aggregates or on Cytodex 3 microcarriers. The data for F3b10 showed that the cell-specific rAb production rate (Qs
rAb) increased in parallel with increases in the specific growth rate (). A similar result was obtained for suspended aggregate cultures of both recombinant BHK cell lines. In contrast, for microcarrier cultures of both BHK cell lines, Qs
product increased as decreased. This report shows that the relationship between cell growth and Qs
product for the cell lines and products studied is dependent upon the culture process. In systems where recombinant cells are growing as a single cell suspension or within a natural suspension aggregate, Qs
product increased with increases in . In such systems, the cells have a rounded morphology. When cells were grown on microcarriers, Qs
product decreased as increased. Cells growing attached to a surface are flat and elongated. The observed differences in the relationship of Qs
product to are correlated with changes in cell morphology. The relationship between Qs
product and is also affected by the choice of cell line.
Correspondence to: A. J. Racher 相似文献
3.
N. G. Krylova T. A. Kulahava S. V. Koran G. N. Semenkova 《Cell and Tissue Biology》2017,11(3):220-226
The effect of coenzyme Q10 on glioma-cell proliferation under serum-deprived conditions has been studied. Our results have shown that the addition of coenzyme Q10 into a serum-free culture medium enhances cell viability, stimulates cell growth, restores mitochondrial potential, and increases the quantity of energized mitochondria. It is found that coenzyme Q10-induced glioma-cell proliferation in conditions of serum deficiency is a result of an intracellular reduced glutathione concentration with subsequent activation of protein kinase C, ERK1/2, and phosphoinositol-3-kinase. 相似文献
4.
G. Radhakrishnamacharya Peeyush Chandra M. R. Kaimal 《Bulletin of mathematical biology》1981,43(2):151-163
The hydrodynamical problem of flow in proximal renal tubule is investigated by considering axisymmetric flow of a viscous,
incompressible fluid through a long narrow tube of varying cross-section with reabsorption at the wall. Two cases for reabsorption
have been studied (i) when the bulk flow,Q, decays exponentially with the axial distancex, and (ii) whenQ is an arbitrary function ofx such thatQ-Q
0 can be expressed as a Fourier integral (whereQ
0 is the flux atx=0). The analytic expressions for flow variables have been obtained by applying perturbation method in terms of wall parameter
ε. The effects of ε on pressure drop across the tube, radial velocity and wall shear have been studied in the case of exponentially
decaying bulk flow and it has been found that the results are in agreement with the existing ones for the renal tubules. 相似文献
5.
The patterns of diurnal variations in pigmentation and optical cross-section were compared for two cyclostat cultures of Chlorella pyrenoidosa, where the dynamics of the photoperiod differed. Populations were light-limited, nutrient rich and growing on an 8:16 light-dark (LD) cycle. One light regime was an 8 h sine function of the light period (sinusoidal culture), while the second had an 1 h sine function super-imposed on the 8 hour sine function (oscillating sinusoidal culture). Hourly samples were taken throughout a 12 h period including the light period. Determinations were made of chlorophyll (Chl) a and b abundance, in vivo absorption spectra, cell number and volume and used to derive both cell-specific (cell) and optical chlorophyll specific (chl) cross sections, as well as the absorption efficiency, Q, of the cells. The results indicate that C. pyrenoidosa is capable of adapting to dynamics in light intensity within an 8 h photoperiod. The sinusoidal culture showed a constant decrease in the Chl a/b ratio of 28% while the total Chl content per cell increased slightly and chl and Q remained constant, suggesting coordinated changes in reaction centers and light harvesting complexes. Over the oscillating photoperiod, however, the second culture displayed a diurnal variation in Chl a/b ratio, a 20% increase in chl and an apparent oscillation in Q. These observations suggest that an oscillating photoperiod promoted the capability of Chl molecules to collect light and that the fractional area of all Chl molecules exposed to the photon flux is inversely related to the photon flux. 相似文献
6.
Cellular Microcystin Content in N-Limited Microcystis aeruginosa Can Be Predicted from Growth Rate 总被引:1,自引:0,他引:1
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Cell quotas of microcystin (QMCYST; femtomoles of MCYST per cell), protein, and chlorophyll a (Chl a), cell dry weight, and cell volume were measured over a range of growth rates in N-limited chemostat cultures of the toxic cyanobacterium Microcystis aeruginosa MASH 01-A19. There was a positive linear relationship between QMCYST and specific growth rate (μ), from which we propose a generalized model that enables QMCYST at any nutrient-limited growth rate to be predicted based on a single batch culture experiment. The model predicts QMCYST from μ, μmax (maximum specific growth rate), QMCYSTmax (maximum cell quota), and QMCYSTmin (minimum cell quota). Under the conditions examined in this study, we predict a QMCYSTmax of 0.129 fmol cell−1 at μmax and a QMCYSTmin of 0.050 fmol cell−1 at μ = 0. Net MCYST production rate (RMCYST) asymptotes to zero at μ = 0 and reaches a maximum of 0.155 fmol cell−1 day−1 at μmax. MCYST/dry weight ratio (milligrams per gram [dry weight]) increased linearly with μ, whereas the MCYST/protein ratio reached a maximum at intermediate μ. In contrast, the MCYST/Chl a ratio remained constant. Cell volume correlated negatively with μ, leading to an increase in intracellular MCYST concentration at high μ. Taken together, our results show that fast-growing cells of N-limited M. aeruginosa are smaller, are of lower mass, and have a higher intracellular MCYST quota and concentration than slow-growing cells. The data also highlight the importance of determining cell MCYST quotas, as potentially confusing interpretations can arise from determining MCYST content as a ratio to other cell components. 相似文献
7.
Raúl González Gustavo Ferrín Ana B. Hidalgo Pedro López-Cillero Mónica Santos-Gónzalez Javier Briceño Miguel A. Gómez José M. Villalba Manuel de la Mata Jordi Muntané 《Chemico-biological interactions》2009,181(1):95-755
d-Galactosamine (d-GalN) induces reactive oxygen species (ROS) generation and cell death in cultured hepatocytes. The aim of the study was to evaluate the cytoprotective properties of N-acetylcysteine (NAC), coenzyme Q10 (Q10) and the superoxide dismutase (SOD) mimetic against the mitochondrial dysfunction and cell death in d-GalN-treated hepatocytes. Hepatocytes were isolated from liver resections. NAC (0.5 mM), Q10 (30 μM) or MnTBAP (Mn(III)tetrakis(4-benzoic acid) porphyrin chloride (1 mg/mL) were co-administered with d-GalN (40 mM) in hepatocytes. Cell death, oxidative stress, mitochondrial transmembrane potential (MTP), ATP, mitochondrial oxidized/reduced glutathione (GSH) and Q10 ratios, electronic transport chain (ETC) activity, and nuclear- and mitochondria-encoded expression of complex I subunits were determined in hepatocytes. d-GalN induced a transient increase of mitochondrial hyperpolarization and oxidative stress, followed by an increase of oxidized/reduced GSH and Q10 ratios, mitochondrial dysfunction and cell death in hepatocytes. The cytoprotective properties of NAC supplementation were related to a reduction of ROS generation and oxidized/reduced GSH and Q10 ratios, and a recovery of mitochondrial complexes I + III and II + III activities and cellular ATP content. The co-administration of Q10 or MnTBAP recovered oxidized/reduced GSH ratio, and reduced ROS generation, ETC dysfunction and cell death induced by d-GalN. The cytoprotective properties of studied antioxidants were related to an increase of the protein expression of nuclear- and mitochondrial-encoded subunits of complex I. In conclusion, the co-administration of NAC, Q10 and MnTBAP enhanced the expression of complex I subunits, and reduced ROS production, oxidized/reduced GSH ratio, mitochondrial dysfunction and cell death induced by d-GalN in cultured hepatocytes. 相似文献
8.
Simon J. Mountford Rachel Daly Eva M. Campi Anjali Bhagwat Andrea J. Robinson Milton T. W. Hearn 《Journal of molecular recognition : JMR》2014,27(5):285-295
A new set of ligands based on substituted pyridine and other N‐heterocyclic structures, possessing an aliphatic primary amino group tether and an exocyclic sulphur atom, has been prepared and immobilized onto epoxy‐activated matrices such as Sepharose 6 Fast Flow®. The derived adsorbents have been evaluated for their utility to capture and purify humanized monoclonal antibodies. Favourable binding properties were assessed from screening assays to determine optimal conditions for the capture and elution of the monoclonal antibodies. Static and dynamic binding experiments were employed to derive the equilibrium dissociation constants KD's and binding capacities Qmax's. Typically, the KD values were in the range of 2–5 μM and the Qmax values between 20 and 75 mg mAb/ml resin, depending on the stereo‐electronic properties of the substituent in the N‐heterocyclic ring structure. The effect of ligand structure on the selectivity of these adsorbents was also investigated, and criteria for their use in the purification of monoclonal antibodies from cell culture supernatants established. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
9.
Summary Ubiquinone-10 (Q10) production was measured in batch cultures of Paracoccus denitrificans grown for 8 h at increasing oxygen concentrations (0–21 % O2 in the sparging gas). Whereas the cellular level of Q10 decreased monotonically from 1.2 to 0.5 mol/g d.w., the total yield of Q10 was maximal at 2.5 % O2 and amounted to 350 nmol (0.3 mg) per L of culture. 相似文献
10.
Tiebo Cai Andrew Black Rachhpal S. Jassal Kai Morgenstern Zoran Nesic 《International journal of biometeorology》2009,53(2):135-148
A simple top-down model of canopy photosynthesis (P) was developed and tested in this study. The model (referred to as the Qe-MM model) is P = αQ
e
P
max/(αQ
e
+ P
max), α and P
max are quantum-use efficiency and potential P, respectively. Q
e is given by Q
d
0 + kQ
b
0, where Q
d
0 and Q
b
0 are the diffuse and direct photosynthetically active radiation (PAR) incident on the canopy, respectively. Q
e can be considered to be the effective incident PAR contributing to P and k is a measure of the contribution of Q
b
0 to Q
e. When k = 1, the Qe-MM model becomes the regular Michaelis-Menten type model of P (referred to as the MM model). A major objective of this study was to determine how well the Qe-MM model could estimate P of a 56-year-old coastal Douglas-fir stand. To this end, we parameterized the Qe-MM model using five and half years of eddy-covariance measurements of CO2 flux above the Douglas-fir stand. The Qe-MM model, with the incorporation of a function of air temperature, accounted for 74% of the variance in over 34,000 half-hourly
P measurements. P estimated using the Qe-MM model had no systematic errors with respect to Q
d
0. Although the Qe-MM model has only one more parameter than the MM model, it accounted for 30% more variance in P than the latter when total incident PAR exceeded 900 μmol m−2 s−1. On average, k was found to be 0.22. We show that this small value of k reflects the significant effect of the scattering of the solar beam and the fraction of light-limited sunlit leaves. We also
show that the success of the Qe-MM model was due to the fact that a large fraction of the sunlit leaves were light-limited as a result of their orientation
to the solar beam. 相似文献
11.
Rym Ben Dhiab Hatem Ben Ouada Hamadi Boussetta Fabrice Franck Amor Elabed Michel Brouers 《Journal of applied phycology》2007,19(4):293-301
The effect of salt concentration (NaCl) on growth, fluorescence, photosynthetic activities and pigment content of the cyanobacterium
Arthrospira platensis has been investigated over 15 days. It has been observed that high NaCl concentration induces an increase of the growth,
photosynthetic efficiency (α), phycobilin/chlorophyll ratio and a slight decrease of dark respiration and compensation points.
Moreover, high NaCl concentration enhances photosystem II (PSII) activity compared to photosystem I (PSI). Results show that
the phycobilin-PSII energy transfer compared to the chlorophyll-PSII (F695,600/F695,440) increases. However, data obtained about the maximal efficiency of PSII photochemistry are controversial. Indeed, the Fv/Fm
ratio decreases in salt adapted cultures, while at the same time the trapping flux per PSII reaction center (TR0/RC) and the probability of electron transport beyond QA (0) remain unchanged at the level of the donor and the acceptor sites of PSII. This effect can be attributed to the interference
of phycobilin fluorescence with Chl a when performing polyphasic transient measurements. 相似文献
12.
Chlamydomonas reinhardtii Dang, was grown in a chemostat culture under phosphate limitation. The steady state concentration of phosphate was below the detection limit (< 1 μg P/L) in all runs. The cellular content of phosphorus (Qp), polyphosphate (Qpp) and chlorophyll a increased with increasing dilution rate, and the growth rate of the alga was described by Qp as well as Qpp in the Droop model. The ratio Qpp/Qp and the activity of alkaline phosphatase were maximal at high and low growth rates, respectively. Palmelloids of Chlamydomonas were found at high dilution rates (D > 0.12 h?1) and became attached to the wall of the culture vessel. They differed from the vegetative stage in both chemical composition and growth rate. Their contents of phosphorus and chlorophyll a were low, as in the vegetative cells, which grew at a low growth rate, whereas the ration Qpp/Qp and the activity of alkaline phosphatase were comparable with those of fast growing vegetative cells. The growth rate of the palmelloids was 0.03 h?1 whereas maximum growth rate (μm) for the vegetative cells was 0.21 h?1. 相似文献
13.
The effect of individual environmental conditions (pH, pO2, temperature, salinity, concentration of ethanol, propanol, tryptone and yeast extract) on the specific growth rate as well
as ethanol and glycerol production rate of Saccharomyces cerevisiae S288C was mapped during the fermentative growth in aerobic auxo-accelerostat cultures. The obtained steady-state values of
the glycerol to ethanol formation ratio (0.1 mol mol−1) corresponding to those predicted from the stoichiometric model of fermentative yeast growth showed that the complete repression
of respiration was obtained in auxostat culture and that the model is suitable for calculation of Y
ATP and Q
ATP values for the aerobic fermentative growth. Smooth decrease in the culture pH and dissolved oxygen concentration (pO2) down to the critical values of 2.3 and 0.8%, respectively, resulted in decrease in growth yield (Y
ATP) and specific growth rate, however the specific ATP production rate (Q
ATP) stayed almost constant. Increase in the concentration of biomass (>0.8 g dwt l−1), propanol (>2 g l−1) or NaCl (>15 g l−1) lead at first to the decrease in the specific growth rate and Q
ATP, while Y
ATP was affected only at higher concentrations. The observed decrease in Q
ATP was caused by indirect rather than direct inhibition of glycolysis. The increase in tryptone concentration resulted in an
increase in the specific growth rate from 0.44 to 0.62 h−1 and Y
ATP from 12.5 to 18.5 mol ATP g dwt−1. This study demonstrates that the auxo-accelerostat method, besides being an efficient tool for obtaining the culture characteristics,
provides also decent conditions for the experiments elucidating the control mechanisms of cell growth. 相似文献
14.
Govindjee 《Photosynthesis research》1990,25(3):151-160
It is well known that two photosystems, I and II, are needed to transfer electrons from H2O to NADP+ in oxygenic photosynthesis. Each photosystem consists of several components: (a) the light-harvesting antenna (L-HA) system, (b) the reaction center (RC) complex, and (c) the polypeptides and other co-factors involved in electron and proton transport. First, we present a mini review on the heterogeneity which has been identified with the electron acceptor side of Photosystem II (PS II) including (a) L-HA system: the PS II and PS II units, (b) RC complex containing electron acceptor Q1 or Q2; and (c) electron acceptor complex: QA (having two different redox potentials QL and QH) and QB (QB-type; Q'B type; and non-QB type); additional components such as iron (Q-400), U (Em,7=–450 mV) and Q-318 (or Aq) are also mentioned. Furthermore, we summarize the current ideas on the so-called inactive (those that transfer electrons to the plastoquinone pool rather slowly) and active reaction centers. Second, we discuss the bearing of the first section on the ratio of the PS II reaction center (RC-II) and the PS I reaction center (RC-I). Third, we review recent results that relate the inactive and active RC-II, obtained by the use of quinones DMQ and DCBQ, with the fluorescence transient at room temperature and in heated spinach and soybean thylakoids. These data show that inactive RC-II can be easily monitored by the OID phase of fluorescence transient and that heating converts active into inactive centers.Abbreviations DCBQ
2,5 or 2,6 dichloro-p-benzoquinone
- DMQ
dimethylquinone
- QA
primary plastoquinone electron acceptor of photosystem II
- QB
secondary plastoquinone electron acceptor of photosystem II
- IODP
successive fluorescence levels during time course of chlorophyll a fluorescence: O for origin, I for inflection, D for dip or plateau, and P for peak 相似文献
15.
M. Bekers E. Ventina J. Laukevics E. Kaminska D. Upite A. Vigants 《Engineering in Life Science》1997,17(3):265-275
In this work, an immobilization method for polymer-levan production by a non-flocculating Z mobilis culture was developed. The extent of cell attachment to the stainless steel wire surface, culture growth and product synthesis were described. It was established that during short-term passive immobilization of non-flocculation Z mobilis cells on a stainless steel wire surface, sufficient amounts of biomass for proper levan and ethano fermentation could not be obtained. Adherence of cells was improved by pressing the paste-like biomass within stainless steel spheres knitted from wire with subsequent dehydration. Biomass fixed in metal spheres was used for repeated batch fermentation of levan. The activation period of cells within wire spheres (WS) was 48 h in duration. During this time, cell growth stabilized at production levels of ethanol and levan of Qeth = 1.238 g/l × h and qeth = 0.47 g/l × h; Qeth = 0.526 g/l × h and qeth = 0.20 g/l × h. Five stable fermentation cycles were realized using one wire sphere inoculum, and maintaining a stable ratio of 2.4 of biomass suspended in the medium to biomass fixed in the sphere. Using fixed Z mobilis biomass in the WS, the total amount of inoculum could be reduced for batch fermentation. Large plaited wire spheres with biomass may have potential in fermentation in viscous systems, including levan production. 相似文献
16.
Summary The effect of a deficiency of inorganic phosphate on the growth rate and on the invertase and phosphatase activities inSaccharomyces carlsbergensis was studied in a chemostat culture using a synthetic medium in which ethanol was the sole carbon source.The kinetic relationship between the growth rate and both the rates of phosphate uptake and the ethanol consumption agreed well with the threshold model but not the multicative model. The invertase activity of the yeast increased as the dilution rate decreased. As the phosphate concentration in the feed was reduced, the enzyme synthesis increased remarkably. Acid phosphatase activity was repressed completely above a critical molecular ratio, 0.015, of monopotassium phosphate to ethanol in the feed medium. As the phosphate concentration in the feed decreased, the maximum specific enzyme activity increased and the corresponding optimum dilution rate decreased. These experimental changes in enzyme synthesis were expressed mathematically using the modified operon models for enzyme regulation in terms of two fractions of limited inorganic phosphate; one which affects growth and the other which is incorporated in excess by the cells.Nomenclature A
ethanol concentration in the culture (mM)
- a, b, c, d
exponents in the operon model
- D
dilution rate (h–1)
- E
enzyme concentration in the culture (enzyme unit l–1)
- Ka, Kb, Kc, Kd, k
equilibrium constants used in the operon model, see Toda (1976b)
- o
operator gene
- P
inorganic phosphate concentration in the culture (mM)
- Pi
limited inorganic phosphate concentration in the cells (mmole inorganic phosphate/g dry weight of cell)
- Q
specific enzyme activity, no units: (E/X)/(E/X)max
- Qc, Qd
as defined in Eq. 12
- R
repressor
- r
regulator gene
- X
cell concentration in the culture (dry cell weight l–1)
Greek Letters
molecular ratio of inorganic phosphate to ethanol in the feed medium (mole/mole)
-
specific growth rate (h–1)
-
A
specific uptake rate of ethanol (mmole/g cell·h)
-
P
specific uptake rate of inorganic phosphate (mmole/g cell·h)
Suffix crit
critical value
- f
feed
- max
maximum
- min
minimum
- t
total
- 1, 2
number of species
Superfix eff
effective for cell growth
- exc
excess
- str
structural 相似文献
17.
Yosepha Shahak Christof Klughammer Ulrich Schreiber Etana Padan Inge Herrman Günter Hauska 《Photosynthesis research》1994,39(2):175-181
The reduction by sulfide of exogenous ubiquinone is compared to the reduction of cytochromes in chromatophores of Rhodobacter capsulatus. From titrations with sulfide values for Vmax of 300 and 10 moles reduced/mg bacteriochlorophyll a·h, and for Km of 5 and 3 M were estimated, for decyl-ubiquinone-and cytochrome c-reduction, respectively. Both reactions are sensitive to KCN, as has been found for sulfide-quinone reductase (SQR) in Oscillatoria limnetica, which is a flavoprotein. Effects of inhibitors interfering with quinone binding sites suggest that at least part of the electron transport from sulfide in R. capsulatus employs the cytochrome bc
1-complex via the ubiquinone pool.Abbreviations BChl a
bacteriochlorophyll a
- DAD
diaminodurene
- decyl-UQ
decyl-ubiquinone
- LED
light emitting diode
- NQNO
2-n-nonyl-4-hydroxyquinoline-N-oxide
- PQ-1
plastoquinone 1
- SQR
sulfide-quinone reductase (E.C. 1.8.5.'.)
- UQ
ubiquinone 10
- Qc
the quinone reduction site on the cytochrome b
6
f/bc
1, complex (also termed Qi or Qr or Qn)
- Qs
the quinone reduction site on SQR
- Qz
quinol oxidation site on the b
6
f/bc
1, complex (also termed Qo or Qp) 相似文献
18.
Rodrigues RC Felipe MG Roberto IC Vitolo M 《Bioprocess and biosystems engineering》2003,26(2):103-107
Batch fermentation of sugarcane bagasse hemicellulosic hydrolyzate by the yeast Candida guilliermondii FTI 20037 was performed using controlled pH values (3.5, 5.5, 7.5). The maximum values of xylitol volumetric productivity (Q
p=0.76 g/l h) and xylose volumetric consumption (Q
s=1.19 g/l h) were attained at pH 5.5. At pH 3.5 and 7.5 the Q
p value decreased by 66 and 72%, respectively. Independently of the pH value, Y
x/s decreased with the increase in Y
p/s suggesting that the xylitol bioconversion improves when the cellular growth is limited. At the highest pH value (7.5), the maximum specific xylitol production value was the lowest (q
pmax=0.085 g/l h.), indicating that the xylose metabolism of the yeast was diverted from xylitol formation to cell growth.List of symbols
P
max
xylitol concentration (g/l)
-
Q
x
volumetric cell production rate (g/l h)
-
Q
s
volumetric xylose uptake rate (g/l h)
-
Q
p
volumetric xylitol production rate (g/l h)
-
q
pmax
specific xylitol production (g/g h)
-
q
smax
specific xylose uptake rate (g/g h)
-
max
specific cell growth rate (h–1)
-
Y
p/s
xylitol yield coefficient, g xylitol per g xylose consumed (g/g)
-
Y
p/x
xylitol yield coefficient, g xylitol per g dry cell mass produced (g/g)
-
Y
x/s
cell yield coefficient, g dry cell mass per g xylose consumed (g/g)
-
cell
percentage of the cell yield from the theoretical value (%)
-
xylitol
percentage of xylitol yield from the theoretical value (%) 相似文献
19.
The quadrupole moment of formaldazine, H2C=N-N=CH2, has been studied for the trans structure (Ð(C-N-N-C) = = 180) and a series of gauche structures ( > 120). Restricted Hartree-Fock theory, second-order Møller-Plesset theory, and quadratic CI theory have been used in conjunction with the basis sets 6-31G*, 6-31G**, 6-311G** and 6-311++G**. Formaldazine is a quadrupolar molecule with primitive quadrupole moment tensor components of Q
xx
= -22.4, Q
yy
= -20.4 and Q
zz
= -25.6 DÅ at the theoretical level QCISD/6-311++G**. The examination of the theoretical level dependency shows that the reliable computation of a quadrupole moment requires the use of a flexible basis set. A large part of the component Q
zz
= -25.6 DÅ is due to the -system and compares, on a per electron basis, with the Q
zz
value of benzene. Conformational changes of the azines in the range 120° < < 180 have but a minute effect on the energy and are associated with only minor electronic relaxation. These conformational changes alter the quadrupole moment tensor components less than Q
xx
= +0.4, Q
yy
= +1.6 and Q
zz
= -1.0 DÅ at QCISD/6-311++G**//QCISD/6-31G*. The direction of these changes is explained by consideration of the rotation of the CN--systems and a small reduction of the CN bond polarity in the gauche structures. The Q
zz
component of formaldazine is representative of the quadrupole moment tensor component along the direction of the C
2
axis of the azine bridge as such. Hence, the results of this study suggest that azines can engage in strong quadrupole-quadrupole interactions and can be employed as lateral synthons in crystal engineering. Electronic Supplementary Material available. 相似文献
20.
Carbon quality and soil microbial property control the latitudinal pattern in temperature sensitivity of soil microbial respiration across Chinese forest ecosystems
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《Global Change Biology》2018,24(7):2841-2849
Understanding the temperature sensitivity (Q10) of soil organic C (SOC) decomposition is critical to quantifying the climate–carbon cycle feedback and predicting the response of ecosystems to climate change. However, the driving factors of the spatial variation in Q10 at a continental scale are fully unidentified. In this study, we conducted a novel incubation experiment with periodically varying temperature based on the mean annual temperature of the soil origin sites. A total of 140 soil samples were collected from 22 sites along a 3,800 km long north–south transect of forests in China, and the Q10 of soil microbial respiration and corresponding environmental variables were measured. Results showed that changes in the Q10 values were nonlinear with latitude, particularly showing low Q10 values in subtropical forests and high Q10 values in temperate forests. The soil C:N ratio was positively related to the Q10 values, and coniferous forest soils with low SOC quality had higher Q10 values than broadleaved forest soils with high SOC quality, which supported the “C quality temperature” hypothesis. Out of the spatial variations in Q10 across all ecosystems, gram‐negative bacteria exhibited the most importance in regulating the variation in Q10 and contributed 25.1%, followed by the C:N ratio (C quality), fungi, and the fungi:bacteria ratio. However, the dominant factors that regulate the regional variations in Q10 differed among the tropical, subtropical, and temperate forest ecosystems. Overall, our findings highlight the importance of C quality and microbial controls over Q10 value in China's forest ecosystems. Meanwhile, C dynamics in temperate forests under a global warming scenario can be robustly predicted through the incorporation of substrate quality and microbial property into models. 相似文献