共查询到20条相似文献,搜索用时 31 毫秒
1.
The polyphasic patterns of fluorescence induction rise in pea leaves in vivo and after the treatment with ionophores have
been studied using a Plant Efficiency Analyzer. To analyze in detail photosystem II (PS II) electron transfer processes, an
extended PS II model was applied, which included the sums of exponential functions to specify explicitly the light-driven
formation of the transmembrane electric potential (ΔΨ(t)) as well as pH in the lumen (pHL(t)) and stroma (pHS(t)). PS II model parameters and numerical coefficients in ΔΨ(t), pHL(t), and pHS(t) were evaluated to fit fluorescence induction data for different experimental conditions: leaf in vivo or after ionophore
treatment at low or high light intensity. The model imitated changes in the pattern of fluorescence induction rise due to
the elimination of transmembrane potential in the presence of ionophores, when ΔΨ = 0 and pHL(t), pHS(t) changed to small extent relative to control values in vivo, with maximum ΔΨ(t) ∼ 90 mV and ΔΨ(t) ∼ 40 mV for the stationary state at ΔpH ≅ 1.8. As the light intensity was increased from 300 to 1200 μmol m−2 s−1, the heat dissipation rate constants increased threefold for nonradiative recombination of P680+Phe− and by ∼30% for P680+QA−. The parameters ΔΨ, pHS and pHL were analyzed as factors of PS II redox state populations and fluorescence yield. The kinetic mechanism of fluorescence quenching
is discussed, which is related with light-induced lumen acidification, when +QA− and P680+ recombination probability increases to regulate the QA reduction. 相似文献
2.
S. Morris J. Callaghan 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1998,168(5):377-388
The Australian Yabby, Cherax destructor, inhabits occasionally hypoxic water. The respiratory gas, acid-base, metabolite and energetic status of this crayfish was
assessed during progressive hypoxia and during 3 h at a water PO2 of 1.33 kPa. The O2 affinity of haemocyanin from C. destructor was increased by lactate (Δlog P
50/Δlog[lactate] = −0.111) and by Ca (Δlog P
50/Δlog[Ca] = −0.62) but not by urate. While the non-bicarbonate buffering capacity was low (Δ[HCO3
−]/ ΔpH=−4.89) the haemocyanin had a low sensitivity to pH changes (ϕ = −0.33). The crayfish showed a compensatory hyperventilation,
which induced a respiratory alkalosis, until the water O2 partial pressure declined below 2.67 kPa, after which the O2 uptake rate was approximately 10% of normoxic rates. The high haemocyanin-O2 affinity maintained haemolymph O2 content during progressive hypoxia despite the normally low arterial O2 partial pressure of C. destructor. During severe hypoxia, pH decreased but increased lactate aided in maintaining haemocyanin-O2 saturation. The importance of regulated haemocyanin-O2 affinity in hypoxic C. destructor was reduced by lowered metabolism, including reduced cardiac output, and the consequent reduction in O2 requirement. Anaerobiosis became important only at very low PO2 but thereafter proceeded rapidly, supported by a marked hyperglycaemia. There was no depletion of adenylates, even after
3 h of severe hypoxia. The tail muscle of C. destructor held small amounts of glycogen which would sustain anaerobiosis for a only a few hours. Hypometabolism seems an important
hypoxic response but severe hypoxia may encourage the crayfish to breathe air.
Accepted: 26 February 1998 相似文献
3.
Uldis Z. Kalnenieks Juris B. Saulitis Nina I. Galinina Edward E. Liepinś Juris E. Shivinka 《Archives of microbiology》1989,151(3):213-219
Brevibacterium flavum 22LD-P cells were shown to maintain a transmembrane pH gradient (pH) from 0.6 to 1.8–2 units and a transmembrane electric potential difference () from 0 to 200 mV depending on the pH and ionic composition of the incubation medium, grwoth substrate and concentration of cells. decreased from 120–140 mV to 0 when medium pH was lowered from neutral to 5.0–5.5 and increased to 180–200 mV when medium pH was raised to 8–9 in cells utilizing acetate or endogenous substrate. Cells growing on sucrose, kept around 100–120 mV at neutral as well as acidic medium pH. Intracellular pH in the acetate utilizing or endogenously respiring cells was maintained with the range of 8.9 to 5.5 at medium pH ranging from 9.1 to 4.0, respectively. Sucrose grown cells were able to maintain a more stable intracellular pH. Endogenously respiring cells in potassium phosphate buffer at high biomass concentrations maintained larger pH and relatively smaller , than the same cells in diluted suspensions. Cells in sodium phosphate buffer possessed larger and almost no pH, but was still dependent on biomass concentration.The lack of intracellular pH homeostasis and the collapse of at acid medium pH are discussed in the context of cell membrane proton permeability. 相似文献
4.
In order to examine the mediatory role of proton motive force (∆p) or proton ATPase in H2 production by Rhodobacter sphaeroides, ∆p was determined under anaerobic conditions in the dark, and the ATPase activity has been studied in R. sphaeroides strain A-10, isolated from Arzni mineral springs in Armenia. Membrane potential (∆φ) was measured from the distribution of
tetraphenylphosphonium cation; pH gradient (∆pH) was the difference between the external and cytoplasmic pH values, and the
latter was measured by 9-aminoacridine (9-AA) fluorescence changes. At pH 7.5, ∆φ was of −94 mV and the reversed ∆pH was +30 mV,
resulting in ∆p of −64 mV. The addition of N,N′-dicyclohexylcarbodiimide (DCCD), the F0F1–ATPase inhibitor, was not affect ∆φ. It was shown that ∆φ varies nearly linearly with ΔpH, ∆φ increased from −57.1 mV at
pH 6.0 to −103.8 mV at pH 8.0; it was compensated at high external pH by a reversed ∆pH, resulting in a low ∆p under anaerobic-dark
conditions. Intracellular ATP concentrations and energetic charge (EC) were measured to evaluate a metabolism activity of
R. sphaeroides. 相似文献
5.
Roland Glaser 《The Journal of membrane biology》1982,66(1):79-85
Summary In isotonic 30mm NaCl-saccharose solution, human red blood cells with intact membrane and normal inside ionic content (C-state) indicate a transmembrane potential between +30 mV (at pH 7.4) and +46 mV (at pH 5.1). After treatment with amphotericin B or nystatin as ionophores, a Donnan equilibrium (D-state) will be reached with the same potential at pH 5.1 but a sharp drop down to –20 mV will occur at pH 7.4. Concerning the erythrocyte shape at these states, a stomatocyteechinocyte transformation takes place, in correlation with the potential shift. Stomatocytes formed at >+25 mV, echinocytes at <+25 mV. At potentials lower than +5 mV, no further effect can be observed. This process is reversible. Neuraminidase treatment as well as outside EDTA do not influence this process significantly. Human serum albumin in concentrations of 2% stabilizes the stomatocytes. 相似文献
6.
Clostridium sporogenes MD1 grew rapidly with peptides and amino acids as an energy source at pH 6.7. However, the proton motive force (p) was only –25 mV, and protonophores did not inhibit growth. When extracellular pH was decreased with HCl, the chemical gradient of protons (ZpH) and the electrical membrane potential () increased. The p was –125 mV at pH 4.7, even though growth was not observed. At pH 6.7, glucose addition did not cause an increase in growth rate, but increased to –70 mV. Protein synthesis inhibitors also significantly increased . Non-growing, arginine-energized cells had a of –80 mV at pH 6.7 or pH 4.7, but was not detected if the F1F0 ATPase was inhibited. Arginine-energized cells initiated growth if other amino acids were added at pH 6.7, and and ATP declined. At pH 4.7, ATP production remained high. However, growth could not be initiated, and neither nor the intracellular ATP concentration declined. Based on these results, it appears that C. sporogenes MD1 does not need a large p to grow, and p appears to serve as a mechanism of ATP dissipation or energy spilling.Mandatory disclaimer: Proprietary or brand names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product, and exclusion of others that may be suitable. 相似文献
7.
Water relations dynamics during simulated sunflecks at high (36°C) and medium (27°C) temperatures and high and low vapour
pressure deficits beween leaf and air (VPD) were studied on shade-grown Piper auritum H.B. & K. plants, a pioneer tree, common in gaps and clearings of tropical rain forests. The leaves of P. auritum wilt rapidly when exposed to high light. Exposure to high VPD and high light caused substantial and rapid dehydration of
leaves. Dehydration could be prevented under high humidity irrespective of temperature. Water stored in leaf cells served
as initial source for transpiration upon high light exposure. This effect increased with increasing VPD and temperature. The
pronounced decrease in leaf water content over time in high light caused a rapid decrease in leaf water potential (Ψl) and a concomitant increase in water potential gradient (ΔΨ/Δx) between trunk and leaf, yet the high leaf elasticity (small bulk elastic modulus, ε) allowed turgor maintenance under most
conditions. Under high VPD and high temperature, stomata remained open and ΔΨ/Δx frequently exceeded 0.95 MPa · m−1, the cavitation-inducing threshold (ΔΨ/Δx
cav) causing high rates of acoustic emissions from stems and leaf petioles and leading to concomitant losses in hydraulic conductance
per leaf area (k
l). At medium temperature (high VPD), stomatal closure contained xylem embolism by keeping ΔΨ/Δx at or below this threshold. We argue that wilting substantially contributes to creating a sufficient driving force for water
uptake from the soil, and reducing the VPD (through a decrease in radiation load and thus leaf temperature) to avoid excessive
dehydration.
Received: 3 March 1996 / Accepted: 10 November 1996 相似文献
8.
In sunflower (Helianthus annuus L.) grown under controlled conditions and subjected to drought by withholding watering, net photosynthetic rate (P
N) and stomatal conductance (g
s) of attached leaves decreased as leaf water potential (Ψw) declined from −0.3 to −2.9 MPa. Although g
s decreased over the whole range of Ψw, nearly constant values in the intercellular CO2 concentrations (C
i) were observed as Ψw decreased to −1.8 MPa, but C
i increased as Ψw decreased further. Relative quantum yield, photochemical quenching, and the apparent quantum yield of photosynthesis decreased
with water deficit, whereas non-photochemical quenching (qNP) increased progressively. A highly significant negative relationship between qNP and ATP content was observed. Water deficit did not alter the pyridine nucleotide concentration but decreased ATP content
suggesting metabolic impairment. At a photon flux density of 550 μmol m−2 s−1, the allocation of electrons from photosystem (PS) 2 to O2 reduction was increased by 51 %, while the allocation to CO2 assimilation was diminished by 32 %, as Ψw declined from −0.3 to −2.9 MPa. A significant linear relationship between mean P
N and the rate of total linear electron transport was observed in well watered plants, the correlation becoming curvilinear
when water deficit increased. The maximum quantum yield of PS2 was not affected by water deficit, whereas qP declined only at very severe stress and the excess photon energy was dissipated by increasing qNP indicating that a greater proportion of the energy was thermally dissipated. This accounted for the apparent down-regulation
of PS2 and supported the protective role of qNP against photoinhibition in sunflower. 相似文献
9.
M. M. Reddy J. R. Riordan P. M. Quinton 《In vitro cellular & developmental biology. Plant》1988,24(9):905-910
Summary The present investigation was undertaken to examine the usefulness of cultured human sweat duct cells for ion transport and
related studies in the genetic disease, cystic fibrosis. Electrical properties of cultured duct (CD) cells were compared with
electrical properties of microperfused duct (MPD) cells. The resting apical membrane potential (V
a
) of the CD cells was −26.4±0.9 mV,n=158 cells as compared to −24.3±0.6 mV,n=105 of MPD cells. The Na+−K+ pump inhibitor ouabain, when applied to the apical surface of the CD cells and basolateral surface of MPD cells, depolarized
both CD cells (from −28.6±3.6 to −16.8±2.4 mV,n=5) and MPD cells (from −23.8±0.5 mV to −19.5±1.8 mV,n=6). The Na+ conductance inhibitor amiloride applied to the apical surface hyperpolarized the apical membrane potentials (Va) of CD cells and MPD cells by −13.2±1.4 mV,n=43 and −34.3±3.1 mV,n=19), respectively, indicating the presence of amiloride sensitive Na+ channels in both groups of cells. However, the amiloride sensitivity of CD cells was dependent on the age of the culture.
Cl− substitution at the apical side by the impermeant anion gluconate depolarized the V
a
of CD cells and MPD cells by 12.2±0.9 mV,n=32 and 37.9±4.3 mV,n=12, respectively. The effect of β-adrenergic agonist isoproterenol (IPR), was inconsistent. In CD cells, IPR either hyperpolarized
(ΔV
a
=−8.3±1.2mV,n=5) or depolarized (ΔV
a
=8.2±2.3 mV,n=4) or had no effect,n=2. In contrast, most of the MPD cells did not respond to IPR, but three cells had a varied response to IPR. Our results suggest
that CD cells, like MPD cells, retain significant Na+ and Cl− conductances. CD cells seem to have developed a higher sensitivity to β-adrenergic stimulation in tissue culture as compared
to MPD cells.
This work was supported by grants from the National Institutes of Health, Bethesda, MD, DK26547, Getty Oil Co., the Gillette
Co., Cystic Fibrosis Research Inc., and the U.S. National Cystic Fibrosis Foundation. 相似文献
10.
Clostridium acetobutylicum P262 cells that were
growing on lactate and acetate had an NAD-independent lactate dehydrogenase
(iLDH) activity of 200 nmol mg protein−1 min−1.
Ammonium sulfate precipitation and DEAE cellulose caused a 35-fold
purification. Gel filtration indicated that the iLDH had a molecular weight
of approximately 55 kDa, but two bands were always observed. Phenyl sepharose
could not separate the two proteins, and hydroxyapatite caused a complete
loss of activity. The semi-purified iLDH had a Vmax of 13,000 nmol
mg protein−1 min−1 and a K
m
value of 3.5 mM for D-lactate. The Vmax and K
m
values for L-lactate were 300 nmol mg protein−1
min−1 and 0.7 mM. The iLDH had a pH optimum of 7.5, was not
activated by fructose-1,6-bisphosphate (FDP), and could be coupled to either
3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) or
dichlorophenol-indophenol (DCPIP), but not methyl viologen (MV) or benzyl
viologen (BV). The iLDH did not have strong absorbance between 500 and 300
nm, and trichloroacetic acid or acid ammonium sulfate extracts had virtually
no fluorescence at 450 nm. The crude extracts also had MTT-linked butyryl-CoA
dehydrogenase activity (60 nmol mg protein−1
min−1). The NAD-independent butyryl-CoA dehydrogenase eluted
from DEAE-cellulose as two fractions. The yellow fraction was extremely
unstable, but the green fraction could be stored for short periods of time at
5°C. The green-colored butyryl-CoA dehydrogenase had strong absorption at
450 nm, and gel filtration indicated that it had a molecular weight of 90
kDa. The NAD-independent butyryl-CoA dehydrogenase could be coupled to MTT,
DCPIP, or MV, but not BV. Because the NAD-independent lactate and butyryl-CoA
dehydrogenase could both be linked to low potential carriers, these two
enzymes may function as oxidation-reduction system in vivo.
Received: 24 July 1996 / Accepted: 10 September 1996 相似文献
11.
The Ca2+-activated maxi K+ channel was found in the apical membrane of everted rabbit connecting tubule (CNT) with a patch-clamp technique. The mean
number of open channels (NP
o
) was markedly increased from 0.007 ± 0.004 to 0.189 ± 0.039 (n= 7) by stretching the patch membrane in a cell-attached configuration. This activation was suggested to be coupled with the
stretch-activation of Ca2+-permeable cation channels, because the maxi K+ channel was not stretch-activated in both the cell-attached configuration using Ca2+-free pipette and in the inside-out one in the presence of 10 mm EGTA in the cytoplasmic side. The maxi K+ channel was completely blocked by extracellular 1 μm charybdotoxin (CTX), but was not by cytoplasmic 33 μm arachidonic acid (AA). On the other hand, the low-conductance K+ channel, which was also found in the same membrane, was completely inhibited by 11 μm AA, but not by 1 μm CTX. The apical K+ conductance in the CNT was estimated by the deflection of transepithelial voltage (ΔV
t
) when luminal K+ concentration was increased from 5 to 15 mEq. When the tubule was perfused with hydraulic pressure of 0.5 KPa, the ΔV
t
was only −0.7 ± 0.4 mV. However, an increase in luminal fluid flow by increasing perfusion pressure to 1.5 KPa markedly enhanced
ΔV
t
to −9.4 ± 0.9 mV. Luminal application of 1 μm CTX reduced the ΔV
t
to −1.3 ± 0.6 mV significantly in 6 tubules, whereas no significant change of ΔV
t
was recorded by applying 33 μm AA into the lumen of 5 tubules (ΔV
t
=−7.2 ± 0.5 mV in control vs.ΔV
t
=−6.7 ± 0.6 mV in AA). These results suggest that the Ca2+-activated maxi K+ channel is responsible for flow-dependent K+ secretion by coupling with the stretch-activated Ca2+-permeable cation channel in the rabbit CNT.
Received: 21 August 1997/Revised: 20 March 1998 相似文献
12.
O. Brix K. D. Clements R. M. G. Wells 《Journal of comparative physiology. B, Biochemical, systemic, and environmental physiology》1999,169(4-5):329-334
Haemoglobin components were analysed for nine species of New Zealand triplefins and their isoelectric points (pI) ranged
from 5.1 to 7.0. The number of well-expressed isohaemoglobins was larger in shallow-water and tidal pool species, ranging
from four in Grahamina signata to eight in Grahamina capito, and were relatively cathodal. Two strongly anodal isohaemoglobins were expressed in the mid-depth species Ruanoho decemdigitatus and Ruanoho whero, and one in the deeper water species Karalepis stewarti and Forsterygion malcolmi. The red blood cell oxygen-binding properties were determined at 15 °C and 25 °C in the pH range 6.7–7.9 for the shallow-water
species G. capito, the shallow to mid-depth species Forsterygion varium, and the deep-water species F. malcolmi. Oxygen affinity was highest for G. capito and the magnitude of the Bohr effect lower (Δlog P
50/ΔpH = −0.37 at 25 °C, where P
50 is the half-saturation coefficient) compared to the two Forsterygion species (Δlog P
50/ΔpH = −0.52 to −0.59). Further, the cooperativity factor, n
50, was lower in G. capito thus maintaining oxygen transport over a wide range of environmental oxygen pressures. Oxygen binding was similarly influenced
by temperature in both G. capito and F. malcolmi (maximum heat of oxygenation ΔHmax = −27 kJ mol−1 and −37 kJ mol−1, respectively). Thus, triplefin fishes living in shallow, thermally unstable habitats possess a greater number of cathodally
migrating isohaemoglobins, and their red blood cells have a higher oxygen affinity and reduced cooperativity which is less
sensitive to changes in pH than do species occurring in more stable, deeper water habitats. Our analysis of an assemblage
of closely related species circumvents some of the difficulties inherent in studies where interpretation of experimental results
is confounded by phylogeny.
Accepted: 18 March 1999 相似文献
13.
Klebsiella oxytoca M5al is an excellent 1,3-propanediol (1,3-PD) producer, but too much lactic acid yielded greatly lessened the fermentation
efficiency for 1,3-PD. To counteract the disadvantage, four lactate deficient mutants were obtained by knocking out the ldhA gene of lactate dehydrogenase (LDH) of K. oxytoca M5al. The LDH activities of the four mutants were from 3.85 to 6.92% of the parental strain. The fed-batch fermentation of
1,3-PD by mutant LDH3, whose LDH activity is the lowest, was studied. The results showed that higher 1,3-PD concentration,
productivity, and molar conversion rate from glycerol to 1,3-PD can be gained than those of the wild type strain and no lactic
acid is produced under both anaerobic and microaerobic conditions. Sucrose fed during the fermentation increased the conversion
and sucrose added at the beginning increased the productivity. In fed-batch fermentation with sucrose as cosubstrate under
microaerobic conditions, the 1,3-PD concentration, conversion, and productivity were improved significantly to 83.56 g l−1, 0.62 mol mol−1, and 1.61 g l−1 h−1, respectively. Furthermore, 60.11 g l−1 2,3-butanediol was also formed as major byproduct in the broth. 相似文献
14.
Y. R. Abdrakhimova I. M. Andreev A. G. Shugaev 《Russian Journal of Plant Physiology》2011,58(4):567-574
Effects of cyanide-resistant alternative oxidase (AOX) and modulators of plant uncoupling mitochondrial proteins (PUMP) on
respiration rate and generation of transmembrane electric potential (ΔΨ) were investigated during oxidation of various substrates
by isolated mitochondria from etiolated coleoptiles of winter wheat (Triticum aestivum L.). Oxidative phosphorylation in wheat mitochondria during malate and succinate oxidation was quite effective (it was characterized
by high respiratory control ratio as defined by Chance, high ADP/O ratio, and rapid ATP synthesis). Nevertheless, the effectiveness
of oxidative phosphorylation was substantially modulated by operation of energy-dissipating systems. The application of safranin
dye revealed the partial dissipation of ΔΨ during inhibition of cytochrome-mediated malate oxidation by cyanide and antimycin
A and demonstrated the operation of AOX-dependent compensatory mechanism for ΔΨ generation. The complex I of mitochondrial
electron transport chain was shown to play the dominant role in ΔΨ generation and ATP synthesis during AOX functioning upon
inhibition of electron transport through the cytochrome pathway. Effects of linoleic acid (PUMP activator) at physiologically
low concentrations (4–10 μM) on respiration and ΔΨ generation in mitochondria were examined. The uncoupling effect of linoleic
acid was shown in activation of the State 4 respiration, as well as in ΔΨ dissipation; this effect was eliminated in the presence
of BSA but was insensitive to purine nucleotides. The uncoupling effect of linoleic acid was accompanied by reversible inhibition
of AOX activity. The results are discussed with regard to possible physiological role of mitochondrial energy-dissipating
systems in regulation of energy transduction in plant cells under stress conditions. 相似文献
15.
The membrane potential (ΔΨm) dependence of the generation of reactive oxygen species (ROS) in isolated guinea-pig brain mitochondria
respiring on NADH-linked substrates (glutamate plus malate) was addressed. Depolarization by FCCP was without effect on H2O2 formation in the absence of bovine serum albumin (BSA). Addition of BSA (0.025%) to the assay medium hyperpolarized mitochondria
by 6.1 ± 0.9 mV (from 169 ± 3 to 175.1 ± 2.1 mV) and increased the rate of H2O2 formation from 207 ± 4.5 to 312 ± 12 pmol/min/mg protein. Depolarization by FCCP (5–250 nM) in the presence of BSA decreased
H2O2 formation but only to the level observed in the absence of BSA. Rotenone stimulated the formation of H2O2 both in the absence and presence of BSA. It is suggested that H2O2 formation in mitochondria supported by NADH-linked substrates is sensitive to changes in ΔΨm only when mitochondria are highly
polarized and even then, 60% of ROS generation is independent of ΔΨm. This is in contrast to earlier reports on the highly
ΔΨm sensitive ROS formation related to reverse electron flow observed in well-coupled succinate-supported mitochondria.
Special issue dedicated to John P. Blass. 相似文献
16.
Hirabayashi T Goto T Morimoto H Yoshimune K Matsuyama H Yumoto I 《Journal of bioenergetics and biomembranes》2012,44(2):265-272
To elucidate the energy production mechanism of alkaliphiles, the relationship between the rate of proton extrusion via the
respiratory chain and the corresponding ATP synthesis rate was examined in obligately alkaliphilic Bacillus clarkii DSM 8720T and neutralophilic Bacillus subtilis IAM 1026. The oxygen consumption rate of B. subtilis IAM 1026 cells at pH 7 was approximately 2.5 times higher than that of B. clarkii DSM 8720T cells at pH 10. The H+/O ratio of B. clarkii DSM 8720T cells was approximately 1.8 times higher than that of B. subtilis IAM 1026 cells. On the basis of oxygen consumption rate and H+/O ratio, the rate of proton translocation via the respiratory chain in B. subtilis IAM 1026 is expected to be approximately 1.4 times higher than that in B. clarkii DSM 8720T. Conversely, the rate of ATP synthesis in B. clarkii DSM 8720T at pH 10 was approximately 7.5 times higher than that in B. subtilis IAM 1026 at pH 7. It can be predicted that the difference in rate of ATP synthesis is due to the effect of transmembrane
electrical potential (Δψ) on protons translocated via the respiratory chain. The Δψ values of B. clarkii DSM 8720T and B. subtilis IAM 1026 were estimated as −192 mV (pH 10) and −122 mV (pH 7), respectively. It is considered that the discrepancy between
the rates of proton translocation and ATP synthesis between the strains used in this study is due to the difference in ATP
production efficiency per translocated proton between the two strains caused by the difference in Δψ. 相似文献
17.
M. Marchlewicz I. Baranowska-Bosiacka A. Kolasa A. Kondarewicz D. Chlubek B. Wiszniewska 《Biometals》2009,22(6):877-887
Adult male Wistar rats were intoxicated with 1% lead acetate (PbAc) administered in drinking water for nine months, which
amounts to a period five times longer than the duration of one spermatogenesis. There were mitochondrial ultrastructure disorders
of epididymal epithelial cells observed in PbAc-treated rats; also a significant lead-induced decrease in ATP concentration
in epididymal epithelial cells (by 32%, P < 0.05), Adenylate Energy Charge value (AEC) (by 8%, P < 0.05) and an increase in ADP (28.5%, P < 0.05), AMP (27%, P < 0.05) and adenosine (by 56%, P < 0.05). The results were measured using high performance liquid chromatography (HPLC) and detected even at low lead concentrations
in whole blood (M:7.03 μg/dL; Q1–Q3: 2.99–7.65). The function of mitochondria in cultured epididymal epithelial cells of control
and PbAc-treated animals were evaluated using fluorophores: Mitotracker Green FM and JC-1. After incubation with Mitotracker
Green FM, we observed active mitochondria producing bright green fluorescence in the cytoplasm of cultured epididymal epithelial
cells, both in the control group and the Pb-treated animals. Incubation of cultured epididymal epithelial cells of animals
from both groups produced red-orange fluorescence with the mitochondrial JC-1 probe indicating mitochondria with high membrane
potential (ΔΨm > 80–100 mV) and green fluorescence in the mitochondria with low membrane potential (ΔΨm <80 mV). The results
showed that a chronic low-level exposure to lead, even without severe clinical symptoms of contamination, disrupted the ultrastructure
and energy metabolism of mitochondria in epididymal epithelial cells. 相似文献
18.
This study investigated the distribution of bacteria in groundwater from 16 different levels in five boreholes in granite
bedrock down to a maximum of 860 m. Enrichment cultures were used to assay the groups of bacteria present. Autoradiographic
studies with14C- or3H-labeled formate, methanol, acetate, lactate, glucose, sodium bicarbonate, leucine, glutamine, thymidine, orN-acetyl-glucosamine were used to obtain information about bacteria active in substrate uptake. The biofilm formation potential
was studied in one borehole. The chemical environment in the groundwater was anaerobic with an Eh between −112 and −383 mV, a pH usually around 8, and a temperature range of 10.2 to 20.5°C, depending on the depth. The organic
content ranged between <0.5 and 9.5 mg total organic carbon liter−1. Carbon dioxide, hydrogen, hydrogen sulfide, and methane were present in the water. The nitrate, nitrite, and phosphate concentrations
were close to, or below, the detection limits, while there were detectable amounts of NH
4
+
in the range of 4 to 330 μg liter−1. The average total number of bacteria was 2.6×105 bacteria ml−1, as determined with an acridine organge direct-count (AODC) technique. The average number of bacteria that grew on a medium
with 1.5 g liter−1 of organic substrate was 7.7×103 colony-forming units (CFU) ml−1. The majority of these were facultatively anaerobic, gram-negative, nonfermenting heterotrophs. Enrichment cultures indicated
the presence of anaerobic bacteria capable of growth on C-1 compounds and hydrogen, presumably methanogenic bacteria. Most
probable number assays with sulfate and lactate revealed up to 5.6×104 viable sulfate-reducing bacteria per ml. A biofilm development experiment indicated an active attached microbial population.
Active substrate uptake could not be registered with the bulk water populations, except for an uptake of leucine not associated
with growth. The bulk water microbial cells in deep groundwater may be inactive cells detached from active biofilms on the
rock surface. 相似文献
19.
Nikhil H. Gokhale Seth Bradford J. A. Cowan 《Journal of biological inorganic chemistry》2007,12(7):981-987
[Cu2+•Cys-Gly-His-Lys] stimulates thermolysin (TLN) activity at low concentration (below 10 μM) and inhibits the enzyme at higher
concentration, with binding affinities of 2.0 and 4.9 μM, respectively. The metal-free Cys-Gly-His-Lys peptide also stimulates
TLN activity, with an apparent binding affinity of 2.2 μM. Coordination of copper through deprotonated imine nitrogens, the
histidyl nitrogen, and the free N-terminal amino group is consistent with the characteristic absorption spectrum of a Cu2+–amino-terminal copper and nickel binding motif (λ
max ∼ 525 nm). The lack of thiol coordination is suggested by both the absence of a thiol to Cu2+ charge transfer band and electrochemical studies, since the electrode potential (vs. Ag/AgCl) 0.84 V (ΔE = 92 mV) for the Cu3+/2+ redox couple obtained for [Cu2+•Cys-Gly-His-Lys] was found to be in close agreement with that of a related complex [Cu2+•Lys-Gly-His-Lys]+ (0.84 V, ΔE = 114 mV). The N-terminal cysteine appears to be available as a zinc-anchoring residue and plays a critical functional role
since the [Cu2+•Lys-Gly-His-Lys]+ homologue exhibits neither stimulation nor inhibition of TLN. Under oxidizing conditions (ascorbate/O2) the catalyst is shown to mediate the complete irreversible inactivation of TLN at concentrations where enzyme activity would
otherwise be stimulated. The observed rate constant for inactivation of TLN activity was determined as k
obs = 7.7 × 10−2 min−1, yielding a second-order rate constant of (7.7 ± 0.9) × 104 M−1 min−1. Copper peptide mediated generation of reactive oxygen species that subsequently modify active-site residues is the most
likely pathway for inactivation of TLN rather than cleavage of the peptide backbone. 相似文献
20.
Whole-cell patch-clamp techniques were used to measure anion currents through the plasma membrane of protoplasts of mesophyll
cells of expanding pea (Pisum sativum L.) leaves. Voltage-induced changes of the currents could be modelled with single exponential activation and deactivation
kinetics. The anion currents were activated at negative membrane potentials. The time constant of activation, τact, increased from 145 ms at −140 mV to 380 ms at −20 mV. A Boltzmann fit to the activation curve, n∞ (ΔGVm/ΔGmax), yielded a half-activation voltage of +27 mV. Opening and closing rate constants, α and β respectively, were calculated
from the values of τ and n∞. The currents depended on the presence of cytoplasmic Ca2+ concentrations higher than 10−6 M. Including 3 mM MgATP in the intracellular solution resulted in a voltage-dependent inactivation of the anion current.
The conductance-voltage relation resulting from the voltage-dependent activation and inactivation had a maximum at about −25
mV. The relations of the current in pea are discussed with respect to the anion currents in guard cells and suspension-cultured
tobacco cells, and its possible role in growing leaf cells.
Received: 1 March 1996 / Accepted: 16 September 1996 相似文献