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1.
Francis N. Craig 《The Journal of general physiology》1944,27(4):325-338
Manometric measurements were made of oxygen uptake (Q
OO2) and aerobic lactic acid output (QG) by slices of cerebral cortex and medulla oblongata of the cat in the presence of mixtures of 1, 5, and 20 volumes per cent of carbon dioxide in oxygen. The concentrations of NaHCO3 and NaCl in the medium were varied to maintain constant pH and sodium ion concentrations. The calcium ion concentration was 0.0002 M. At pH 7.5 under these conditions, an increase in carbon dioxide from 1 per cent to 5 per cent doubled the QG of both tissues but did not alter Q
OO2; an increase from 5 per cent to 20 per cent carbon dioxide had no further effect on QG in either tissue or Q
OO2 of cortex, but did depress the Q
OO2 of medulla. At pH 8.1, an increase in carbon dioxide from 1 per cent to 5 per cent raised the Q
OO2 and QG of cortex by about 60 per cent. Measurements at low oxygen tension carried out previously in phosphate medium were repeated in bicarbonate medium to obtain data for the combined output of lactic acid and carbon dioxide (QA). When the oxygen in the gas phase was decreased from 95 to 3 volumes per cent, the lactic acid output as measured colorimetrically increased by 114 mg./gm. in cortex and by 8 mg./gm. in medulla; QA increased from 12.3 to 13.5 in cortex and decreased from 5.1 to 3.8 in medulla. 相似文献
2.
The Mechanism of the Calorigenic Action of Thyroid Hormone : Stimulation of Na+ + K+-activated adenosinetriphosphatase activity 总被引:1,自引:0,他引:1
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In an earlier study, we proposed that thyroid hormone stimulation of energy utilization by the Na+ pump mediates the calorigenic response. In this study, the effects of triiodothyronine (T3) on total oxygen consumption (QOO2), the ouabain-sensitive oxygen consumption [QOO2(t)], and NaK-ATPase in liver, kidney, and cerebrum were measured. In liver, ~90% of the increase in QOO2 produced by T3 in either thyroidectomized or euthyroid rats was attributable to the increase in QOO2(t). In kidney, the increase in QOO2(t) accounted for 29% of the increase in QOO2 in thyroidectomized and 46% of the increase in QOO2 in euthyroid rats. There was no demonstrable effect of T3 in euthyroid rats on QOO2 or QOO2(t) of cerebral slices. The effects of T3 on NaK-ATPase activity in homogenates were as follows: In liver +81% from euthyroid rats and +54% from hypothyroid rats. In kidney, +21% from euthyroid rats and +69% from hypothyroid rats. T3 in euthyroid rats produced no significant changes in NaK-ATPase or Mg-ATPase activity of cerebral homogenates. Liver plasma membrane fractions showed a 69% increase in NaK-ATPase and no significant changes in either Mg-ATPase or 5'-nucleotidase activities after T3 injection. These results indicate that thyroid hormones stimulate NaK-ATPase activity differentially. This effect may account, at least in part, for the calorigenic effects of these hormones. 相似文献
3.
Isolated epithelial cells of the toad bladder. Their preparation, oxygen consumption, and electrolyte content 总被引:2,自引:0,他引:2
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Epithelial cells of the toad bladder were disaggregated with EDTA, trypsin, hyaluronidase, or collagenase and were then scraped free of the underlying connective tissue. In most experiments EDTA was complexed with a divalent cation before the tissue was scraped. Q
OO2, sucrose and inulin spaces, and electrolytes of the isolated cells were measured. Cells disaggregated by collagenase or hyaluronidase consumed O2 at a rate of 4 µl hr-1 dry wt-1. Q
OO2 was increased 50% by ADH (100 U/liter) or by cyclic 3'',5''-AMP (10 mM/liter). Na+-free Ringer''s depressed the Q
OO2 by 40%. The Q
OO2 of cells prepared by trypsin treatment or by two EDTA methods was depressed by Na+-free Ringer''s but was stimulated relatively little by ADH. Two other EDTA protocols produced cells that did not respond to Na+ lack or ADH. The intracellular Na+ and K+ concentrations of collagenase-disaggregated cells were 32 and 117 mEq/kg cell H2O, respectively. Cation concentrations of hyaluronidase cells were similar, but cells that did not respond to ADH had higher intracellular Na+ concentrations. Cells unresponsive to ADH and Na+ lack had high sucrose spaces and low transcellular membrane gradients of Na+, K+, and Cl-. The results suggest that trypsin and EDTA disaggregation damage the active Na+ transport system of the isolated cell. Certain EDTA techniques may also produce a general increase in permeability. Collagenase and hyaluronidase cells appear to function normally. 相似文献
4.
The metabolism of rat retina was found to be sensitive to the concentration of the carbon dioxide-bicarbonate buffer system. Increasing the carbon dioxide from 1 per cent to 5 per cent at constant pH nearly doubled both respiration and glycolysis. Increasing the carbon dioxide at constant pH from 5 per cent to 20 per cent had no effect on glycolysis, but depressed the Q
OO2 from 31 to 19. In a medium containing glucose and the 1 per cent carbon dioxide-bicarbonate buffer, the addition of succinate increased the Q
OO2 from 12 to 26, without affecting glycolysis. In a medium containing glucose and phosphate, succinate had no significant effect. 相似文献
5.
The initial burst of respiratory activity (Qo2) of imbibing soybean (Glycine max [L.] Merr. var. Wayne) seed tissue is cyanide-insensitive, and sensitive to salicylhydroxamate: presumptive evidence for the presence of alternate respiration. The initial O2 consumption is also highly sensitive to propyl gallate. Soybean lipoxygenase exhibits similar characteristics of insensitivity to cyanide and sensitivity to salicylhydroxamate and to propyl gallate. The initial burst of respiration is enhanced by the addition of linoleic acid, a lipoxygenase substrate. These results indicate that the conventional tests for alternate respiration in plant tissues can be confounded by lipoxygenase; they also suggest that propyl gallate can be used to assess the possible participation of lipoxygenase in the O2 uptake by plant tissues. 相似文献
6.
T. J. B. Stier 《The Journal of general physiology》1935,19(2):339-350
The time for the appearance of the cytochrome C absorption band after shaking a suspension of bakers'' yeast with various O2-N2 mixtures was determined at each of six temperatures. At each temperature a linear relation between this interval—called the reduction time—and O2 tension was found. It was shown: 1. That under our experimental conditions, absorption bands of cytochrome were seen when the O2 tension of the suspension was reduced to, or below, a certain pressure which was found to be specific for each temperature (this pressure is provisionally considered to be identical with or very near to the "critical O2 tension" usually found in Q
OO2-O2-tension relationships); 2. That the x-axis intercept obtained from the reduction time - O2-tension plot gives the value of the "critical" O2 pressure at each temperature; 3. That the O2 tension within the suspension is reduced by the respiratory activity of the yeast cells. An equation describing these observations is given and is used in calculating rates of O2 consumption from measurements of reduction time of cytochrome. The average difference between the calculated values and the manometric measurements of Q
OO2 was found to be 6.6 per cent. A rapid optical method of measuring rates of O2 consumption based on the findings of these experiments is proposed for use with cytochrome-containing microorganisms. 相似文献
7.
Endothelial dysfunction causes an imbalance in endothelial NO and O2− production rates and increased peroxynitrite formation. Peroxynitrite and its decomposition products cause multiple deleterious effects including tyrosine nitration of proteins, superoxide dismutase (SOD) inactivation, and tissue damage. Studies have shown that peroxynitrite formation during endothelial dysfunction is strongly dependent on the NO and O2− production rates. Previous experimental and modeling studies examining the role of NO and O2− production imbalance on peroxynitrite formation showed different results in biological and synthetic systems. However, there is a lack of quantitative information about the formation and biological relevance of peroxynitrite under oxidative, nitroxidative, and nitrosative stress conditions in the microcirculation. We developed a computational biotransport model to examine the role of endothelial NO and O2− production on the complex biochemical NO and O2− interactions in the microcirculation. We also modeled the effect of variability in SOD expression and activity during oxidative stress. The results showed that peroxynitrite concentration increased with increase in either O2− to NO or NO to O2− production rate ratio (QO2−/QNO or QNO/QO2−, respectively). The peroxynitrite concentrations were similar for both production rate ratios, indicating that peroxynitrite-related nitroxidative and nitrosative stresses may be similar in endothelial dysfunction or inducible NO synthase (iNOS)-induced NO production. The endothelial peroxynitrite concentration increased with increase in both QO2−/QNO and QNO/QO2− ratios at SOD concentrations of 0.1–100 μM. The absence of SOD may not mitigate the extent of peroxynitrite-mediated toxicity, as we predicted an insignificant increase in peroxynitrite levels beyond QO2−/QNO and QNO/QO2− ratios of 1. The results support the experimental observations of biological systems and show that peroxynitrite formation increases with increase in either NO or O2− production, and excess NO production from iNOS or from NO donors during oxidative stress conditions does not reduce the extent of peroxynitrite mediated toxicity. 相似文献
8.
Effects of water vapor pressure deficit on photochemical and fluorescence yields in tobacco leaf tissue
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Peterson RB 《Plant physiology》1990,92(3):608-614
The relationship between photochemical quantum yield (s) and fluorescence yield have been investigated in leaf tissue from Nicotiana tabacum using CO2 exchange and a modulated fluorescence measuring system. The quantum yield of CO2 fixation at 1.6% (v/v) O2 and limiting irradiance was reduced 20% by increasing the mean H2O vapor pressure deficit (VPD) from 9.2 to 18.6 mbars. As [CO2] and irradiance were varied, the intrinsic quantum yield of open photosystem II units (s/qQ where qQ is the photochemical fluorescence quenching coefficient) declined linearly with the degree of nonphotochemical fluorescence quenching. The slope and y-intercept values for this function were significantly reduced when the mean VPD was 18.4 millibars relative to 8.9 millibars. Susceptibility of the leaf tissue to photoinhibition was unaffected by VPD. Elevated O2 concentrations (20.5% v/v) reduced the intrinsic quantum yield of net CO2 uptake due to the occurrence of O2-reducing processes. However, the relative effect of high VPD compared to low VPD on intrinsic quantum yield was not dependent on the O2 level. This suggests that the Mehler reaction does not mediate the response of quantum yield to elevated VPD. The results are discussed with regard to the possible role of transpiration stress in regulating dissipation of excitation by electron transport pathways other than noncyclic electron flow supporting reduction of CO2 and/or O2. 相似文献
9.
《Comparative biochemistry and physiology. A, Comparative physiology》1996,113(3):293-296
To better understand how tissue specific metabolic rates might contribute to the maintenance of elevated body temperatures in green turtles (Chelonia mydas), we determined the effect of temperature on oxygen consumption of green fat, small intestine, nonswimming skeletal muscle, pectoralis muscle, liver, heart, and kidney tissues from 5–35°C. We found a direct relationship between tissue metabolic rate (microliters of O2/g wet mass per hour) and temperature in all tissues measured except for green fat. The Q10 values ranged from 0.65 to 3.38. There were significant differences in metabolic rate among tissues as well as in how temperature influenced tissue metabolic rates. Tissue metabolic rates were highest in kidney and heart tissues. Green fat and small intestine had the lowest and most temperature-insensitive values. Muscle tissue had a high oxygen consumption relative to other reptiles, and this elevated metabolism may provide a functional advantage for long distance swimming and heat production. 相似文献
10.
Oxygen consumption rates (QO2) of laboratory reared stage one zoeae of Pandalus borealis (Krøyer) at 1.5, 3, 4.5, 6, and 9°C were 1.5, 2.2, 2.6, 3.6 and 4.1μ O2 · mg?1 · h?1, respectively. These values of QO2 correspond to 0.26, 0.38, 0.44, 0.60, and 0.70 μl O2 · individual?1 · h?1. At 10.5 °C oxygen consumption rates decreased suggesting thermally induced respiratory stress.The equation log10QO2 = 0.55 log10T°C + 0.086 describes the relationship between QO2 (μl O2 · mg?1 · h?1) and sea-water temperature between 1.5 and 9°C. Corresponding values of QO2 for an individual (μl O2 · h?1) exhibited the relationship log10QO2 = 0.55 log10T°C ?0.686.The minimum daily metabolic caloric requirements for an individual zoea ranged from 0.04 at 3 °C to 0.07 calories per day at 8 °C. The number of calories ingested daily ranged from 0.4 to 0.5 at 3 to 8 °C. 相似文献
11.
E Cadenas A Boveris C I Ragan A O Stoppani 《Archives of biochemistry and biophysics》1977,180(2):248-257
Complex I (NADH-ubiquinone reductase) and Complex III (ubiquinol-cytochrome c reductase) supplemented with NADH generated O2? at maximum rates of 9.8 and 6.5 nmol/min/mg of protein, respectively, while, in the presence of superoxide dismutase, the same systems generated H2O2 at maximum rates of 5.1 and 4.2 nmol/min/mg of protein, respectively. H2O2 was essentially produced by disproportionation of O2?, which constitutes the precursor of H2O2. The effectiveness of the generation of oxygen intermediates by Complex I in the absence of other specific electron acceptors was 0.95 mol of O2? and 0.63 mol of H2O2/mol of NADH. A reduced form of ubiquinone appeared to be responsible for the reduction of O2 to O2?, since (a) ubiquinone constituted the sole common major component of Complexes I and III, (b) H2O2 generation by Complex I was inhibited by rotenone, and (c) supplementation of Complex I with exogenous ubiquinones increased the rate of H2O2 generation. The efficiency of added quinones as peroxide generators decreased in the order Q1 > Q0 > Q2 > Q6 = Q10, in agreement with the quinone capacity of acting as electron acceptor for Complex I. In the supplemented systems, the exogenous quinone was reduced by Complex I and oxidized nonenzymatically by molecular oxygen. Additional evidence for the role of ubiquinone as peroxide generator is provided by the generation of O2? and H2O2 during autoxidation of quinols. In oxygenated buffers, ubiquinol (Q0H2), benzoquinol, duroquinol and menadiol generated O2? with k3 values of 0.1 to 1.4 m? · s?1 and H2O2 with k4 values of 0.009 to 4.3 m?1 · s?1. 相似文献
12.
The assimilation of ammonium by the N-limited green alga Selenastrum minutum results in the suppression of photosynthetic electron flow from H2O to CO2 (6, 7, 18). In this study, results are presented which describe the correponding change in steady-state chlorophyll a fluorescence. The addition of ammonium resulted in a transient decline in fluorescence followed by a marked increase. Fluorescence did not return to control levels until the added ammonium had been assimilated. Analysis of the fluorescence transients showed that ammonium assimilation resulted in a rapid increase in nonphotochemical quenching (Qe) peaking 10 to 15 seconds after ammonium addition. Qe then decreased dramatically reaching a minimum value approximately 45 seconds following ammonium addition and returned to the control level only after the added ammonium had been assimilated. There were no effects of ammonium addition on photochemical quenching (Qq) for approximately 10 to 15 seconds at which time both gross O2 evolution (as measured by mass spectrometry) and Qq declined. In the presence of d,l-glyceraldehyde or when cells were held at the CO2 compensation point, the addition of ammonium resulted in a decline in Qe 10 to 15 seconds after addition. The Qe peak and the Qq decline were absent. These results imply that the transient increase in Qe and the subsequent decline in Qq may be attributed to the decline in Calvin cycle activity during ammonium assimilation. The decline in Qe is apparently a direct result of ammonium assimilation. The observation that the Qe peak precedes the Qq decline would be consistent with the decreases in Calvin cycle carbon flow occurring at the kinase reactions prior to glyceraldehyde-3-phosphate dehydrogenase. 相似文献
13.
《Journal of Biomedical Engineering》1990,12(4):309-315
The studies were performed to elucidate the mechanism underlying the neural damage which may occur during prolonged electrical stimulation of either brain tissue or peripheral nerve. The partial pressure of oxygen (pO2) was measured in the sciatic nerve and the cerebral cortex of adult cats before and during direct, local electrical stimulation of these neural tissues, using stimulus parameters capable of inducing neural injury. pO2 was monitored by the polarographic method, employing a platinum microelectrode inserted into the tissue adjacent to or beneath the stimulating electrode. In the sciatic nerve there was no marked change in intrafascicular pO2 in three cats upon initiation of the electrical stimulation. In a fourth animal intraneural pO2 increased briefly upon intitiation of the stimulation. In no case did the intrafascicular compartment of nerves become significantly hypoxic. In the cerebral cortex, the start of stimulation was accompanied by a significant increase (approximately 12–15 Torr) in intracortical pO2 beneath the stimulating electrode, and pO2 remained at or above the pre-stimulus value for the duration of the stimulation. These results show that extracellular hypoxia is unlikely to be a significant factor in the neural injury induced in brain or peripheral nerve by prolonged electrical stimulation. 相似文献
14.
David W Hicks Robert F McMahon 《Journal of experimental marine biology and ecology》2002,277(1):61-78
The respiratory responses to increasing temperature and progressive hypoxia were examined relative to temperature acclimation in the nonindigenous, brown mussel, Perna perna (Mytilidae) from the Gulf of Mexico. When oxygen uptake rate (V?O2) was recorded at near full air O2 saturation, rate-temperature curves for Texas specimens of P. perna were sigmoidal, V?O2 generally increasing with increasing temperature but becoming suppressed as temperatures approached 10 and 30 °C, corresponding closely to this species' incipient thermal limits. At each tested temperature, V?O2 did not differ among individuals acclimated to 15, 20, or 25 °C. Lack of thermal acclimation was also reflected in acclimatory Q10 values>1.0 (range=1.34-2.14) recorded across acclimation groups at test temperatures equivalent to acclimation temperature. Low acute respiratory Q10 values in all acclimation groups across 15-20 °C indicated a limited capacity for thermal regulation of V?O2 within this temperature range. The ability of P. perna to regulate O2 uptake with progressive hypoxia was temperature-dependent, increasing from poor O2 regulation at 10 °C to good regulation at 30 °C. The O2 regulatory ability of P. perna and other open-water mytilids in declining O2 concentrations does not greatly differ from that of estuarine heterodont bivalves, suggesting that it is not a major factor preventing open-water species, such as P. perna, from invading estuarine environments. However, P. perna's inability to regulate O2 uptake at temperatures>25 °C combined with its relatively low upper thermal limit of 30 °C will likely prevent it from establishing permanent estuarine populations on Gulf of Mexico shores. 相似文献
15.
Augusto CingolaniEffendy Fabio Marchetti Claudio PettinariRiccardo Pettinari Brian W SkeltonAllan H White 《Inorganica chimica acta》2002,329(1):100-112
Silver(I) acylpyrazolonate derivatives of formula [Ag(Q)(R3P)]2 and [Ag(Q)(R3P)2], (QH=1-phenyl-3-methyl-4-R′(CO)-pyrazol-5-one; QOH, R′=furane; QSH, R′=thiophene; R=Ph, Cy, o-tol), have been synthesised and characterised, both in the solid state and in solution. The derivatives [Ag(Q)(R3P)]2 contain dinuclear AgO2NP units with the acylpyrazolonate coordinating in a bridging O,O′-Q-N fashion. The [Ag(Q)(R3P)2] are tetrahedral species, with the distortion from ideal geometry increasing with the bulk of the phosphine. The [Ag(Q)(R3P)2] derivatives are fluxional in chloroform solution when R3P is sterically hindered (R=Cy or o-tol), dissociating partially to the [Ag(Q)(R3P)] fragment and free R3P. [Ag(QS)(Ph3P)]2 reacts with 1-methyl-2-mercaptoimidazole (Hmimt) affording the compound [Ag(Hmimt)(Ph3P)(QS)] and [Ag(QO)(Ph3P)]2 reacts with 1-methyl-imidazole (Meim) affording the compound [Ag(Meim)(Ph3P)(QO)], whereas [Ag(QS)(Ph3P)]2 reacts with 1,10-phenanthroline (phen), affording the compound [Ag(phen)(Ph3P)](QS). Finally [Ag(QS)(Ph3P)2] reacts with phen producing the ionic species [Ag(phen)(Ph3P)2](QS). 相似文献
16.
Active Transport of Inorganic Carbon Increases the Rate of O(2) Photoreduction by the Cyanobacterium Synechococcus UTEX 625 总被引:4,自引:4,他引:0
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Chlorophyll a fluorescence of Synechococcus UTEX 625 was quenched during the transport of inorganic carbon, even when CO2 fixation was inhibited by iodoacetamide. Measurements with a pulse modulation fluorometer showed that at least 75% of the quenching was due to oxidation of Qa, the primary acceptor of photosystem II. Mass spectrometry revealed that transport of inorganic carbon increased the rate of O2 photoreduction. Hence, O2 could serve as an electron acceptor to allow oxidation of Qa even in the absence of CO2 fixation. 相似文献
17.
Summary A phenomenon associated with the aging process is a general age-dependent decline in cellular bioenergetic capacity that varies
from tissue to tissue and even from cell to cell within the same tissue. This variation eventually forms a tissue bioenergy
mosaic. Recent evidence by our group suggests that the accumulation of mitochondrial DNA mutations, in conjunction with a
concurrent decrease in full-length mtDNA in tissues such as skeletal and cardiac muscle, strongly correlates with decreased
mitochondrial function and accounts for the bioenergy mosaic. Evidence is also presented suggesting that amelioration with
coenzyme Q10 may restore some of the age-associated decline in bioenergy function, in effect providing the potential for a “redox therapy”.
Coenzyme Q is a naturally occurring material that is present in the membranes of all animal cells. Its primary function is
to act as an electron carrier in the mitochondrial electron transport chain enabling the energy from substrates such as fats
and sugars (in the form of reducing equivalents) to be ultimately captured in the form of ATP, which in turn may be utilised
as a source of cellular bioenergy. Coenzyme Q10 has no known toxic effects and has been used in a limited number of animal studies and human clinical trials; however, the
mechanism of action of coenzyme Q10 remains unclear. A series of experiments by this group aimed at determining the efficacy of coenzyme Q10 treatment on ameliorating the bioenergy capacity at the organ and cellular level will also be reviewed. 相似文献
18.
Gunnar Brix Mona Salehi Ravesh Stefan Zwick Jürgen Griebel Stefan Delorme 《Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB)》2012,28(2):119-128
Concentration-time courses measured by dynamic contrast-enhanced (DCE) imaging can be described by a convolution of the arterial input with an impulse response function, QT(t), characterizing tissue microcirculation. Data analysis is based on two different approaches: computation of QT(t) by algebraic deconvolution (AD) and subsequent evaluation according to the indicator dilution theory (IDT) or parameterization of QT(t) by analytical expressions derived by compartmental modeling. Pitfalls of both strategies will be addressed in this study.Tissue data acquired by DCE-CT in patients with head-and-neck cancer and simulated by a reference model (MMID4) were analyzed by a two-compartment model (TCM), a permeability-limited two-compartment model (PL-TCM) and AD. Additionally, MMID4 was used to compute the ‘true’ response function that corresponds to the simulated tumor data.TCM and AD yielded accurate fits, whereas PL-TCM performed worse. Nevertheless, the corresponding response functions diverge markedly. The response curves obtained by TCM decrease exponentially in the early perfusion phase and overestimate the tissue perfusion, QT(0). AD also resulted in response curves starting with a negative slope and not – as the ‘true’ response function in accordance with the IDT – with a horizontal plateau. They are thus not valid responses in the sense of the IDT that can be used unconditionally for parameter estimation.Response functions differing considerably in shape can result in virtually identical tissue curves. This non-uniqueness makes a strong argument not to use algebraic but rather analytical deconvolution to reduce the class of solutions to representatives that are in accordance with a-priori knowledge. To avoid misinterpretations and systematic errors, users must be aware of the pitfalls inherent to the different concepts. 相似文献
19.
Claudio Pettinari Fabio Marchetti Paolo Natanti Sergey Semenov Vladislav Zolin 《Inorganica chimica acta》2006,359(12):4063-4070
Synthesis and spectroscopic characterization of new lanthanide complexes [Ln(QAD)3(EtOH)(H2O)], (Ln = Tb, Eu; HQAD = 1-phenyl-3-methyl-4-adamantylcarbonyl-pyrazol-5-one), [H3O][Tb(QAD)4], [Ln(QAD)3(N-N)] (Ln = Tb, Eu; N-N = 1,10-phenanthroline (Phen), 2,2′-bipyridyl (Bipy), 4,4′-dimethyl-2,2′-bipyridyl (4,4′-Me2Bipy)) are reported. The crystal structures of the proligand HQAD and of complexes [H3O][Tb(QAD)4] and [Tb(QAD)3(4,4′-Me2Bipy)] have been determined. In both complexes the lanthanide ions are in a square antiprismatic environment, the H3O+ cation in the former acid complex being stabilized by H-bonding. Luminescence studies have been performed on selected derivatives. 相似文献
20.
We have used the desiccation-tolerant lichen Flavoparmelia caperata, containing the green algal photobiont Trebouxia gelatinosa, to examine H/D isotope effects in Photosystem II in vivo. Artifact-free H/D isotope effects on both PSII primary charge separation and water oxidation yields were determined as a function of flash rate from chlorophyll-a variable fluorescence yields. Intact lichens could be reversibly dehydrated/re-hydrated with H2O/D2O repeatedly without loss of O2 evolution, unlike all isolated PSII preparations. Above a threshold flash rate, PSII charge separation decreases sharply in both D2O and H2O, reflecting loss of excitation migration and capture by PSII. Changes in H/D coordinates further slow charge separation in D2O (?23% at 120?Hz), attributed to reoxidation of the primary acceptor QA?. At intermediate flash rates (5–50?Hz) D2O decreases water oxidation efficiency (O2 evolution) by ?2–5%. No significant isotopic difference is observed at slow flash rates (<5?Hz) where charge recombination dominates. Slower D2O diffusion, changes in hydrogen bonding networks, and shifts in the pKa's of ionizable residues may all contribute to these systematic variations of H/D isotope effects. Lichens' reversible desiccation tolerance allows highly reproducible H/D exchange kinetics in PSII reactions to be studied in vivo for the first time. 相似文献