2. |
- Shutova, Tatiana, 1964-, et al.
(författare)
-
The photosystem II-associated Cah3 in Chlamydomonas enhances the O-2 evolution rate by proton removal
- 2008
-
Ingår i: EMBO Journal. - : Wiley. - 0261-4189 .- 1460-2075. ; 27:5, s. 782-791
-
Tidskriftsartikel (refereegranskat)abstract
- Water oxidation in photosystem II ( PSII) is still insufficiently understood and is assumed to involve HCO3-. A Chlamydomonas mutant lacking a carbonic anhydrase associated with the PSII donor side shows impaired O-2 evolution in the absence of HCO3-. The O-2 evolution for saturating, continuous illumination (R-O2) was slower than in the wild type, but was elevated by HCO3- and increased further by Cah3. The R-O2 limitation in the absence of Cah3/HCO3- was amplified by H2O/D2O exchange, but relieved by an amphiphilic proton carrier, suggesting a role of Cah3/HCO3- in proton translocation. Chlorophyll fluorescence indicates a Cah3/HCO3- effect at the donor side of PSII. Time-resolved delayed fluorescence and O-2-release measurements suggest specific effects on proton-release steps but not on electron transfer. We propose that Cah3 promotes proton removal from the Mn complex by locally providing HCO3-, which may function as proton carrier. Without Cah3, proton removal could become rate limiting during O-2 formation and thus, limit water oxidation under high light. Our results underlie the general importance of proton release at the donor side of PSII during water oxidation.
|
|