共查询到20条相似文献,搜索用时 46 毫秒
1.
Svetlana V. Kamzolova Igor G. Morgunov 《Applied microbiology and biotechnology》2013,97(12):5517-5525
The possibility of using rapeseed oil as a carbon source for microbiological production of α-ketoglutaric acid (KGA) has been studied. Acid formation on the selective media has been tested in 26 strains of Yarrowia lipolytica yeast, and the strain Y. lipolytica VKM Y-2412 was selected as a prospective producer of KGA from rapeseed oil. KGA production by the selected strain was studied in dependence on thiamine concentration, medium pH, temperature, aeration, and concentration of oil. Under optimal conditions (thiamine concentration of 0.063 μg?g cells?1, pH?3.5, 30 °C, high dissolved oxygen concentration (pO2) of 50 % (of air saturation), and oil concentration in a range from 20 to 60 g?l?1), Y. lipolytica VKM Y-2412 produced up to 102.5 g?l?1 of KGA with the mass yield coefficient of 0.95 g?g?1 and the volumetric KGA productivity (Q KGA) of 0.8 g?l?1?h?1. 相似文献
2.
The temperature dependences of the P870+Q?A → P870QA and P870+Q?B → P870QB recombination reactions were measured in reaction centers from Rhodopseudomonas sphaeroides. The data indicate that the P870+Q?B state decays by thermal repopulation of the P870+Q?A state, followed by recombination. ΔG° for the P870+Q?A → P870+Q?B reaction is ?6.89 kJ · mol?1, while ΔH° = ?14.45 kJ · mol?1 and ?TΔS° = + 7.53 kJ · mol?1. The activation ethalpy, , for the P870+Q?A Δ P870+Q?B reaction is +56.9 kJ · mol?1, while the activation entropy is near zero. The results permit an estimate of the shape of the potential energy curve for the P870+Q?A → P870+Q?B electron transfer reaction. 相似文献
3.
Cardiac oxidative stress is an early event associated with diabetic cardiomyopathy, triggered by hyperglycemia. We tested the hypothesis that targeting left-ventricular (LV) reactive oxygen species (ROS) upregulation subsequent to hyperglycemia attenuates type 1 diabetes-induced LV remodeling and dysfunction, accompanied by attenuated proinflammatory markers and cardiomyocyte apoptosis. Male 6-week-old mice received either streptozotocin (55 mg/kg/day for 5 days), to induce type 1 diabetes, or citrate buffer vehicle. After 4 weeks of hyperglycemia, the mice were allocated to coenzyme Q10 supplementation (10 mg/kg/day), treatment with the angiotensin-converting-enzyme inhibitor (ACE-I) ramipril (3 mg/kg/day), treatment with olive oil vehicle, or no treatment for 8 weeks. Type 1 diabetes upregulated LV NADPH oxidase (Nox2, p22phox, p47phox and superoxide production), LV uncoupling protein UCP3 expression, and both LV and systemic oxidative stress (LV 3-nitrotyrosine and plasma lipid peroxidation). All of these were significantly attenuated by coenzyme Q10. Coenzyme Q10 substantially limited type 1 diabetes-induced impairments in LV diastolic function (E:A ratio and deceleration time by echocardiography, LV end-diastolic pressure, and LV −dP/dt by micromanometry), LV remodeling (cardiomyocyte hypertrophy, cardiac fibrosis, apoptosis), and LV expression of proinflammatory mediators (tumor necrosis factor-α, with a similar trend for interleukin IL-1β). Coenzyme Q10's actions were independent of glycemic control, body mass, and blood pressure. Coenzyme Q10 compared favorably to improvements observed with ramipril. In summary, these data suggest that coenzyme Q10 effectively targets LV ROS upregulation to limit type 1 diabetic cardiomyopathy. Coenzyme Q10 supplementation may thus represent an effective alternative to ACE-Is for the treatment of cardiac complications in type 1 diabetic patients. 相似文献
4.
Samhan-Arias AK Duarte RO Martín-Romero FJ Moura JJ Gutiérrez-Merino C 《Archives of biochemistry and biophysics》2008,469(2):243-254
Synaptic plasma membranes (SPMV) decrease the steady state ascorbate free radical (AFR) concentration of 1 mM ascorbate in phosphate/EDTA buffer (pH 7), due to AFR recycling by redox coupling between ascorbate and the ubiquinone content of these membranes. In the presence of NADH, but not NADPH, SPMV catalyse a rapid recycling of AFR which further lower the AFR concentration below 0.05 μM. These results correlate with the nearly 10-fold higher NADH oxidase over NADPH oxidase activity of SPMV. SPMV has NADH-dependent coenzyme Q reductase activity. In the presence of ascorbate the stimulation of the NADH oxidase activity of SPMV by coenzyme Q1 and cytochrome c can be accounted for by the increase of the AFR concentration generated by the redox pairs ascorbate/coenzyme Q1 and ascorbate/cytochrome c. The NADH:AFR reductase activity makes a major contribution to the NADH oxidase activity of SPMV and decreases the steady-state AFR concentration well below the micromolar concentration range. 相似文献
5.
The electron-transfer reactions and thermodynamic equilibria involving the quinone acceptor complex in bacterial reaction centers from R. sphaeroides were investigated. The reactions are described by the scheme: We found that the charge recombination pathway of D+QAQ?B proceeds via the intermediate state D+Q?AQB, the direct pathway contributing less than approx. 5% to the observed recombination rate. The method used to obtain this result was based on a comparison of the kinetics predicted for the indirect pathway (given by the product kAD-times the fraction of reaction centers in the Q?AQB state) with the observed recombination rate, kobsD+ →D. The kinetic measurements were used to obtain the pH dependence (6.1 ? pH ? 11.7) of the free energy difference between the states Q?AQB and QAQ?B. At low pH (less than 9) QAQ?B is stabilized relative to Q?AQB by 67 meV, whereas at high pH Q?AQB is energetically favored. Both Q?A and Q?B associate with a proton, with pK values of 9.8 and 11.3, respectively. The stronger interaction of the proton with Q?B provides the driving force for the forward electron transfer. 相似文献
6.
Redox titrations of the flash-induced formation of C550 (a linear indicator of Q?) were performed between pH 5.9 and 8.3 in Chlamydomonas Photosystem II particles lacking the secondary electron acceptor, B. One-third of the reaction centers show a pH-dependent midpoint potential (Em,7.5) = ? 30 mV) for redox couple , which varies by ?60 mV/pH unit. Two-thirds of the centers show a pH-independent midpoint potential (Emm = + 10 mV) for this couple. The elevated pH-independent Em suggests that in the latter centers the environment of Q has been modified such as to stabilize the semiquinone anion, Q?. The midpoint potentials of the centers having a pH-dependent Em are within 20 mV of those observed in chloroplasts having a secondary electron acceptor. It appears therefore that the secondary electron acceptor exerts little influence on the Em of . An EPR signal at g 1.82 has recently been attributed to a semiquinone-iron complex which comprises Q?. The similar redox behavior reported here for C550 and reported by others (Evans, M.C.W., Nugent, J.H.A., Tilling, L.A. and Atkinson, Y.E. (1982) FEBS Lett. 145, 176–178) for the g 1.82 signal in similar Photosystem II particles confirm the assignment of this EPR signal to Q?. At below ?200 mV, illumination of the Photosystem II particles produces an accumulation of reduced pheophytin (Ph?). At ?420 mV Ph? appears with a quantum yield of 0.006–0.01 which in this material implies a lifetime of 30–100 ns for the radical pair P-680+Ph?. 相似文献
7.
We conducted an open-top chamber experiment for 3?years to examine the effect of elevated CO2 and temperature on soil respiration in experimental stands of Quercus glauca, an evergreen tree species common in the warm temperate zone of Japan. Seedlings of Q. glauca were planted in open-top chambers and treated with factorial combinations of ambient and elevated (ambient?×?1.4, ambient?×?1.8) CO2 concentrations and ambient and elevated (+3°C) air temperatures. Elevated CO2 significantly increased the total soil respiration rate (P?<?0.001) and the soil respiration rate at 15°C (R 15) (P?<?0.05) but had no significant effect on the temperature coefficient Q 10. Although temperature significantly affected total soil respiration rate (P?<?0.05), neither the R 15 nor the Q 10 of total soil respiration was affected significantly by the air temperature increase. Annual soil respiration rate, estimated from R 15, Q 10, and soil temperature data, tended to increase with elevated CO2 concentration. These results suggest that soil respiration rate in Japanese warm temperate broad-leaved forests dominated by Q. glauca is sensitive to elevated CO2 and is likely to increase under future climatic conditions. 相似文献
8.
H Roberts W M Choo S C Smith S Marzuki A W Linnane T H Porter K Folkers 《Archives of biochemistry and biophysics》1978,191(1):306-315
The effects of 33 quinone derivatives on mitochondrial electron transfer in yeast were examined. Twenty-two of the compounds were also tested for their effects on the growth of yeast cells. Four strong inhibitors of electron transfer were identified: 5-n-undecyl-6-hydroxy-4, 7-dioxobenzothiazole, 7-ω-cyclohexyloctyl-6-hydroxy-5,8-quinolinequinone, 7-n-hexadecyl-mercapto-6-hydroxy-5, 8-quinolinequinone, and 3-n-dodecylmercapto-2-hydroxy-1, 4-naphthoquinone. They inhibit the growth of yeast with ethanol as an energy source, but not when glucose is the energy source. The NADH oxidase activity of isolated mitochondria is 50% inhibited by these quinone derivatives at about 10?8m, or 0.5 μmol/g mitochondrial protein; 1000-fold higher concentrations do not affect electron transfer from NADH or succinate to coenzyme Q2. The effects of the inhibitors on cytochrome spectra indicate that they block electron transfer between cytochromes b and c1. A possible antagonism between these compounds and coenzyme Q at a site between cytochromes b and C1 is discussed in terms of Mitchell's “protonmotive Q cycle” hypothesis (Mitchell, P. (1976) J. Theor. Biol. 62, 327–367). 6-β-naphthylmercapto-5-chloro-2,3-dimethoxy-1,4-benzoquinone inhibits electron transfer between succinate and coenzyme Q2 or phenazine methosulfate, suggesting a site in the succinate-coenzyme Q reductase complex with a different quinone specificity from that of the site in the cytochrome bc1 complex. Seven of the quinone derivatives inhibit growth on both glucose and ethanol media, indicating that their effect is not the result of inhibition of respiration. 相似文献
9.
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
10.
E. I. Kalenikova E. V. Kharitonova E. A. Gorodetskaya O. G. Tokareva O. S. Medvedev 《Biochemistry (Moscow) Supplemental Series B: Biomedical Chemistry》2014,8(3):267-272
The pharmacokinetics of the total pool of coenzyme Q10 (CoQ10), its oxidized (ubiquinone) and reduced (ubiquinol, CoQ10H2) forms have been investigated in rats plasma during 48 h after a single intravenous injection of a solution of solubilized CoQ10 (10 mg/kg) to rats. Plasma levels of CoQ10 were determined by HPLC with spectrophotometric and coulometric detection. In plasma samples taken during the first minutes after the CoQ10 intravenous injection, the total pool of coenzyme Q10 and proportion of CoQ10H2 remained unchanged during two weeks of storage at ?20°C. The kinetic curve of the total pool of coenzyme Q10 corresponds to a one-compartment model (R 2 = 0.9932), while the corresponding curve of its oxidized form fits to the two-compartment model. During the first minutes after the injection a significant portion of plasma ubiquinone undergoes reduction, and after 7 h the concentration of ubiquinol predominates. The decrease in total plasma coenzyme Q10 content was accompanied by the gradual increase in plasma ubiquinol, which represented about 90% of total plasma CoQ10 by the end of the first day. The results of this study demonstrate the ability of the organism to transform high concentrations of the oxidized form of CoQ10 into the effective antioxidant (reduced) form and justify prospects of the development of parenteral dosage forms of CoQ10 for the use in the treatment of acute pathological conditions. 相似文献
11.
S S Tong Y Hirokata M A Trush E G Mimnaugh E Ginsburg M C Lowe T E Gram 《Biochemical and biophysical research communications》1981,100(3):944-950
The photosystem II electron acceptor 3,6-dichloro-2,5-dimethoxy-p-benzoquinone [DCDMQ] is suggested to replace the second quinone-type two electron acceptor B (or R); the DCDMQ Hill reaction is sensitive to 3-(3,4-dichlorophenyl)-1,1-dimethylurea, but is insensitive to dry heptane extraction of thylakoids and other photosystem II inhibitors. Addition of HCO3? to CO2-depleted thylakoids in silicomolybdate, DCDMQ, diaminodurene and ferricyanide Hill reactions brought about 1,3,10 and 10 fold increase in the electron transport rates; these data confirm that HCO3? affects both Q? to B and B2? to PQ reactions. 相似文献
12.
Although duroquinone had little effect upon NADH oxidation in neutral lipid depleted mitochondria, durohydroquinone was oxidized by ETP at a rate sensitive to antimycin A. Fractionation of mitochondria into purified enzyme systems showed durohydroquinone: cytochromec reductase to be concentrated in NADH: cytochromec reductase, absent in succinate:cytochromec reductase, and decreased in reduced coenzyme Q:cytochromec reductase. Durohydroquinone oxidation could be restored by recombining reduced coenzyme Q:cytochromec reductase with NADH:coenzyme Q reductase. Pentane extraction had no effect upon either durohydroquinone or reduced coenzyme Q10 oxidation, indicating lack of a quinone requirement between cytochromesb andc. Both chloroquine diphosphate and acetone (96%) treatment irreversibly inhibited NADH but not succinate oxidation. Neither reagents had any effect upon durohydroquinone oxidation but both inhibited reduced coenzyme Q10 oxidation 50%, indicating a site of action between Q10 and duroquinone sites. Loss of chloroquine sensitive reduced coenzyme Q10 oxidation after acetone extraction suggests two sites for Q10 before cytochromeb. 相似文献
13.
Jerzy A. Zoladz Micha? ?migielski Joanna Majerczak ?ukasz R. Nowak Justyna Zapart-Bukowska Olgierd Smoleński Jan Kulpa Krzysztof Duda Joanna Drzewińska Grzegorz Bartosz 《Neurochemical research》2012,37(12):2715-2724
In the present study we have evaluated the effect of a single hemodialysis session on the brain-derived neurotrophic factor levels in plasma [BDNF]pl and in serum [BDNF]s as well as on the plasma isoprostanes concentration [F2 isoprostanes]pl, plasma total antioxidant capacity (TAC) and plasma cortisol levels in chronic kidney disease patients. Twenty male patients (age 69.8?±?2.9?years (mean?±?SE)) with end-stage renal disease undergoing maintenance hemodialysis on regular dialysis treatment for 15?C71?months participated in this study. A single hemodialysis session, lasting 4.2?±?0.1?h, resulted in a decrease (P?=?0.014) in [BDNF]s by ~42?% (2,574?±?322 vs. 1,492?±?327?pg?ml?1). This was accompanied by an increase (P?<?10?4) of [F2-Isoprostanes]pl (38?±?3 vs. 116?±?16?pg?ml?1), decrease (P?<?10?4) in TAC (1,483?±?41 vs. 983?±?35 trolox equivalents, ??mol?l?1) and a decrease (P?=?0.004) in plasma cortisol level (449.5?±?101.2 vs. 315.3?±?196.3?nmol?l?1). No changes (P?>?0.05) in [BDNF]pl and the platelets count were observed after a single dialysis session. Furthermore, basal [BDNF]s in the chronic kidney disease patients was significantly lower (P?=?0.03) when compared to the age-matched control group (n?=?23). We have concluded that the observed decrease in serum BDNF level after hemodialysis accompanied by elevated [F2-Isoprostanes]pl and decreased plasma TAC might be caused by enhanced oxidative stress induced by hemodialysis. 相似文献
14.
Closed-system respirometry is a standard technique used to determine aerobic metabolism of aquatic organisms. Open-top systems are rarely used due to concerns of gas exchange across the air–water interface. Here, we evaluated an open-top respirometry system by comparing the mass-specific routine metabolic rate (RMR) of the tropical diadromous finfish barramundi, Lates calcarifer, in both closed-top and open-top respirometers. The RMR of 190?g barramundi was determined across broad temperatures ranging from 18 to 38?°C. There was no significant difference in RMR between barramundi in either closed- or open-top respirometers at any temperature (p?>?0.05). To ensure RMR measurements were not an artifact of the respirometry system, barramundi were reciprocally transplanted into either respective closed-top or open-top respirometer and oxygen consumption re-measured at each temperature treatment. The RMR of transplanted barramundi was found to be virtually identical in either respirometer. RMR increased linearly with increasing temperature; the relationship between RMR and temperature (T; 18–38?°C) can be described as 3.658T?36.294?mg?O2?kg?0.8?h?1. The daily energetic cost of RMR was 1.193T?11.838?kJ?kg?0.8?day?1. Q10 for barramundi increased significantly with increasing temperature (p?0.0001). Q10(18–28) was the lowest at 1.7 and Q10(28–38) the highest at 1.9, over the whole experiment temp range Q10(18–28) was 1.8. The current study demonstrates that open-top respirometry is a reliable and practical alternative to closed-top respirometry for accurate determination of the aerobic metabolism of barramundi and has potential application for a number of different aquatic organisms. 相似文献
15.
Summary The addition of coenzyme Q10 to culture media stimulates the serum-free growth of HeLa, HL-60 cells, and mouse fibroblasts (Balb/3T3). With HeLa cells, the stimulation by coenzyme Q10 is additive to the stimulation by ferricyanide, an impermeable electron acceptor for the transplasma membrane electron transport. This combined response to coenzyme Q10 and ferricyanide is enhanced with insulin. -Tocopherylquinone can also stimulate the growth of HeLa cells, but vitamin K1 is inactive. Specificity of quinone effects is indicated. Serum-free growth of Balb/3T3 and SV 40 transformed BaIb/3T3 (SV/T2) cells is also stimulated by coenzyme Qio with stimulation similar to HeLa cells. However, Balb/3T3 cells are not stimulated by ferricyanide, which does not increase the response to coenzyme Q10. The transformed cells (SV/T2) respond better to ferricyanide alone, but the effects of coenzyme Qio and ferricyanide are not additive. Serum-free growth of HL-60 cells is stimulated dramatically by coenzyme Q10. The extent of growth stimulation on HL-60 cells is almost six-fold that of HeLa or Balb/3T3 cells. The stimulation of NADH-ferricyanide reductase (a transmembrane redox enzyme) by coenzyme Q10 with HL-60 cells is similar to their growth pattern in response to coenzyme Q10. Unlike HL-60, HeLa and Balb/3T3 cells show little stimulation of ferricyanide reduction by coenzyme Q10. The stimulatory effect on both ferricyanide reduction and cell growth by the short side-chain coenzyme Q2 is much less than that of the long side-chain coenzyme Q10. Ferricyanide reduction by HeLa cells is inhibited by coenzyme Q analogs such as 2,3-dimethoxy-5-chloro-6-naphthyl-mercapto-coenzyme Q and 2-methoxy-3-ethoxyl-5-methyl-6-hexadecyl-mercapto-coenzyme Q. However, these inhibitions are reversed by coenzyme Q10. The growth inhibition of HL-60 cells by other coenzyme Q analogs, such as capsiacin can also be reversed by coenzyme Q10. These data indicate that plasma membrane-based NADH oxidation or modification of the membrane quinone redox balance may be a basis for the growth stimulation. 相似文献
16.
To elucidate the role of aquaporins in the control of the root pressure, we tested the effects of HgCl2 (aquaporin blocker) at concentrations from 10?8 to 10?2 M on the exudation rate (J w). Experiments were performed with detached roots of 5–7-day-old etiolated maize (Zea mays L.) seedlings. HgCl2 suppressed exudation by 50–70% at the concentration of 2 × 10?5 M. At the concentration of 2.5 × 10?4 M, HgCl2 reduced J w during first 20–40 min, but in 2 h, it activated exudation by ten and more times. In this case, the root and osmotic pressures of the exudates increased by 1.5 times. The hydraulic conductance reduced approximately by 30% during first 30 min and increased severalfold in 2 h. The temperature coefficient (Q10) of J w attained 14 in 2 h. At the concentration of 10?2 M, HgCl2-induced acceleration of exudation was replaced by its inhibition essentially immediately. We suggested that a driving force for HgCl2-induced stimulation of the J w might be an increase in the osmotic component of the root pressure or the involvement of its nonosmotic (so-called metabolic) component. The results allow a supposition that aquaporins are involved in the control of water transport in the root. 相似文献
17.
J. G. Kerr M. C. Eimers I. F. Creed M. B. Adams F. Beall D. Burns J. L. Campbell S. F. Christopher T. A. Clair F. Courchesne L. Duchesne I. Fernandez D. Houle D. S. Jeffries G. E. Likens M. J. Mitchell J. Shanley H. Yao 《Biogeochemistry》2012,111(1-3):393-409
Within the southeast Canada and northeast USA region, a peak in sulphate (SO4 2?) concentration has been reported for some streams following periods of substantial catchment drying during the summer months (ON, Canada; VT, NH and NY, USA). However, it is currently unclear if a SO4 2? response to seasonal drying is widespread across the broader region, or to what extent the level of response varies among catchments. In our study, SO4 2? response to seasonal drying was compared in 20 catchments from 11 locations across southeastern Canada (ON, QC and NS) and northeastern USA (NH, NY, VT, WV and ME). Using long-term monitoring data of stream discharge and chemistry, the number of days for each month of the dry season (# d) when discharge (Q) was below a threshold level (25th percentile; Q25) was calculated for each catchment to give a measure of ‘seasonal dryness’ (# d Q < Q25). A SO4 2? response score (rs) was then calculated for each catchment based on linear regression analysis of # d Q < Q25 versus either the annual SO4 2? concentration, or the residual of annual SO4 2? concentration as a function of time (year). The final rs values for each catchment provided an estimate of the proportion of variation in annual SO4 2? concentration which could be explained by seasonal drying (possible rs range = 0–1). Of the 20 catchments, 13 exhibited some level of a SO4 2? response to seasonal drying (rs = 0.04–0.72) with an additional two catchments exhibiting a SO4 2? response for one or more seasons. SO4 2? response scores were positively related to percent wetland area (w) (rs = 1.000 ? 0.978e?0.054* w , r 2 = 0.44) and percent saturated area (sat) (rs = 0.481 ? 0.488e?0.101* sat, r 2 = 0.54) indicating that wetlands/saturated areas were an important driver of regional variation in the SO4 2? response to seasonal drying. Our results suggest that any shift towards drier summers as a result of climate change could impact SO4 2? dynamics in a large number of catchments throughout the region. 相似文献
18.
Electro-optical characterization of the photoreceptor disk membrane vesicle is performed by examining the electric field and concentration dependence of the steady-state birefringence of aqueous suspensions of the vesicles. The electric polarizability anisotropy is found to be negative and of large magnitude: α1 ?α2 = ?(1?3) × 10?10 cm3. The optical anisotropy is determined to be also negative but of small magnitude: g1 ?g2 = ?1 × 10?7. The specific Kerr constant deduced from the concentration dependence of the Kerr constant is found to be very large: Ksp = 7 × 10?4 c.s.u. Upon deforming the vesicles osmotically from the spherical shell to the disk structure, the steady-state birefringence increases by an order of magnitude which is attributed solely to the increase in optical anisotropy attending the corresponding change in the geometric eccentricity of the vesicle. A plausible birefringence mechanism based on the known structural features of the vesicles is proposed, which would account for these findings. 相似文献
19.
Yuki Kato Tadao Shibamoto Shoichi Yamamoto Tadashi Watanabe Naoko Ishida Miwa Sugiura Fabrice Rappaport Alain Boussac 《BBA》2012,1817(11):1998-2004
Ca2+ and Cl? ions are essential elements for the oxygen evolution activity of photosystem II (PSII). It has been demonstrated that these ions can be exchanged with Sr2+ and Br?, respectively, and that these ion exchanges modify the kinetics of some electron transfer reactions at the Mn4Ca cluster level (Ishida et al., J. Biol. Chem. 283 (2008) 13330–13340). It has been proposed from thermoluminescence experiments that the kinetic effects arise, at least in part, from a decrease in the free energy level of the Mn4Ca cluster in the S3 state though some changes on the acceptor side were also observed. Therefore, in the present work, by using thin-layer cell spectroelectrochemistry, the effects of the Ca2+/Sr2+ and Cl?/Br? exchanges on the redox potential of the primary quinone electron acceptor QA, Em(QA/QA?), were investigated. Since the previous studies on the Ca2+/Sr2+ and Cl?/Br? exchanges were performed in PsbA3-containing PSII purified from the thermophilic cyanobacterium Thermosynechococcus elongatus, we first investigated the influences of the PsbA1/PsbA3 exchange on Em(QA/QA?). Here we show that i) the Em(QA/QA?) was up-shifted by ca. + 38 mV in PsbA3-PSII when compared to PsbA1-PSII and ii) the Ca2+/Sr2+ exchange up-shifted the Em(QA/QA?) by ca. + 27 mV, whereas the Cl?/Br? exchange hardly influenced Em(QA/QA?). On the basis of the results of Em(QA/QA?) together with previous thermoluminescence measurements, the ion-exchange effects on the energetics in PSII are discussed. 相似文献