Abstract
The primary electron donor P-680 of the Photosystem-II reaction center was photoxidized by a short flash given after dark adaptation of photosynthetic membranes in which oxygen evolution was inhibited. The P-680+ reduction rate was measured under different conditions of pH and salt concentration by following the recovery of the absorption change at 820 nm. As previously reported for Tris-washed chloroplasts (Conjeaud, H., and P. Mathis, 1980, Biochim. Biophys. Acta, 590:353-359) a fast phase of P-680+ reduction slows down as the bulk pH decreases. When salt concentration increases, this fast phase becomes faster for pH above 4.5-5 and slower below. A quantitative interpretation is proposed in which the P-680+ reduction kinetics by the secondary electron donor Z are controlled by the local pH. This pH, at the membrane level, can be calculated using the Gouy-Chapman theory. A good fit of the results requires to assume that the surface charge density of the inside of the membrane, near the Photosystem-II reaction center, is positive at low pH values and becomes negative as the pH increases, with a local isoelectric point ∼4.8. These results lead us to propose a functional scheme in which a pH-dependent proton release is coupled to the electron transfer between secondary and primary donors of Photosystem-II. The H+/e ratio varies from 1 at low pH to 0 at high pH, with a real pK ∼6.5 for the protonatable species.
Full text
PDF
Selected References
These references are in PubMed. This may not be the complete list of references from this article.
- Babcock G. T., Blankenship R. E., Sauer K. Reaction kinetics for positive charge accumulation on the water side of chloroplast photosystem II. FEBS Lett. 1976 Jan 15;61(2):286–289. doi: 10.1016/0014-5793(76)81058-7. [DOI] [PubMed] [Google Scholar]
- Babcock G. T., Sauer K. A rapid, light-induced transient in electron paramagnetic resonance signal II activated upon inhibition of photosynthetic oxygen evolution. Biochim Biophys Acta. 1975 Feb 17;376(2):315–328. doi: 10.1016/0005-2728(75)90024-9. [DOI] [PubMed] [Google Scholar]
- Babcock G. T., Sauer K. The rapid component of electron paramagnetic resonance signal II: a candidate for the physiological donor to photosystem II in spinach chloroplasts. Biochim Biophys Acta. 1975 Feb 17;376(2):329–344. doi: 10.1016/0005-2728(75)90025-0. [DOI] [PubMed] [Google Scholar]
- Barber J. Membrane surface charges and potentials in relation to photosynthesis. Biochim Biophys Acta. 1980 Dec;594(4):253–308. doi: 10.1016/0304-4173(80)90003-8. [DOI] [PubMed] [Google Scholar]
- Brand J. J., Becker D. W. Evidence for direct roles of calcium in photosynthesis. J Bioenerg Biomembr. 1984 Aug;16(4):239–249. doi: 10.1007/BF00744278. [DOI] [PubMed] [Google Scholar]
- Conjeaud H., Mathis P., Paillotin G. Primary and secondary electron donors in photosystem II of chloroplasts. Rates of electron transfer and location in the membrane. Biochim Biophys Acta. 1979 May 9;546(2):280–291. doi: 10.1016/0005-2728(79)90046-x. [DOI] [PubMed] [Google Scholar]
- Conjeaud H., Mathis P. The effects of pH on the reductions kinetics of P-680 in Tris-treated chloroplasts. Biochim Biophys Acta. 1980 May 9;590(3):353–359. doi: 10.1016/0005-2728(80)90206-6. [DOI] [PubMed] [Google Scholar]
- Haveman J., Mathis P. Flash-induced absorption changes of the primary donor of photosystem II at 820 nm in chloroplasts inhibited by low pH or tris-treatment. Biochim Biophys Acta. 1976 Aug 13;440(2):346–355. doi: 10.1016/0005-2728(76)90069-4. [DOI] [PubMed] [Google Scholar]
- Itoh S. Membrane surface potential and the reactivity of the system II primary electron acceptor to charged electron carriers in the medium. Biochim Biophys Acta. 1978 Nov 9;504(2):324–340. doi: 10.1016/0005-2728(78)90180-9. [DOI] [PubMed] [Google Scholar]
- Lakhdar-Ghazal F., Tichadou J. L., Tocanne J. F. Effect of pH and monovalent cations on the ionization state of phosphatidylglycerol in monolayers. An experimental (surface potential) and theoretical (Gouy-Chapman) approach. Eur J Biochem. 1983 Aug 15;134(3):531–537. doi: 10.1111/j.1432-1033.1983.tb07599.x. [DOI] [PubMed] [Google Scholar]
- Masamoto K., Itoh S., Nishimura M. Salt-induced pH changes in spinach chloroplast suspension. Changes in surface potential and surface pH of thylakoid membranes. Biochim Biophys Acta. 1980 Jun 10;591(1):142–152. doi: 10.1016/0005-2728(80)90228-5. [DOI] [PubMed] [Google Scholar]
- Nakatani H. Y., Barber J. Further studies of the thylakoid membrane surface charges by particle electrophoresis. Biochim Biophys Acta. 1980 Jun 10;591(1):82–91. doi: 10.1016/0005-2728(80)90222-4. [DOI] [PubMed] [Google Scholar]
- Reinman S., Mathis P., Conjeaud H., Stewart A. Kinetics of reduction of the primary donor of photosystem II. Influence of pH in various preparations. Biochim Biophys Acta. 1981 Apr 13;635(2):429–433. doi: 10.1016/0005-2728(81)90040-2. [DOI] [PubMed] [Google Scholar]
- Sonneveld A., Rademaker H., Duysens L. N. Chlorophyll a fluorescence as a monitor of nanosecond reduction of the photooxidized primary donor P-680 Of photosystem II. Biochim Biophys Acta. 1979 Dec 6;548(3):536–551. doi: 10.1016/0005-2728(79)90063-x. [DOI] [PubMed] [Google Scholar]
- Yamamoto Y., Ke B. Membrane-surface electric properties of triton-fractionated spinach subchloroplast fragments. Biochim Biophys Acta. 1981 Jul;636(2):175–184. doi: 10.1016/0005-2728(81)90091-8. [DOI] [PubMed] [Google Scholar]
- Yerkes C. T., Babcock G. T. Surface charge asymmetry and a specific calcium ion effect in chloroplast photosystem II. Biochim Biophys Acta. 1981 Jan 14;634(1):19–29. doi: 10.1016/0005-2728(81)90124-9. [DOI] [PubMed] [Google Scholar]
- van Best J. A., Mathis P. Kinetics of reduction of the oxidized primary electron donor of photosystem II in spinach chloroplasts and in Chlorella cells in the microsecond and nanosecond time ranges following flash excitation. Biochim Biophys Acta. 1978 Jul 6;503(1):178–188. doi: 10.1016/0005-2728(78)90170-6. [DOI] [PubMed] [Google Scholar]