FAST-ELECTRON TRANSFER FROM CYTOCHROME C(6) AND PLASTOCYANIN TO PHOTOSYSTEM-I OF CHLAMYDOMONAS-REINHARDTII REQUIRES PSAF

TO study the function of the PsaF subunit of photosystem I (PSI), the interactions between plastocyanin or cytochrome c(6) and PSI isolated from wild-type and a PsaF-deficient mutant of Chlamydomonas reinhardti i have been examined using cross-linking techniques and flash absorpti on spectroscopy. We show that efficient electron transfer from both pl astocyanin and cytochrome c(6) to PSI depends on PsaF. A remarkable fe ature of the PSI complex of C. reinhardtii is that both plastocyanin a nd cytochrome c(6) reduce P700(+) with first-order kinetics and a half -time of 3 mu s, which is unique among photosynthetic organisms examin ed.