Abstract
Ferredoxin-NADP-oxidoreductase (FNR) catalyzes NADPH production by photosystem I in the presence of ferredoxin. A part of FNR in the chloroplast is stably associated with the purified thylakoids and is fractionated with cytochrome b6f complex in higher plants, suggesting its possible involvement in the cyclic electron transport. Here we have estimated the amount of FNR in the thylakoids purified from wild type and various photosynthetic mutants of Chlamydomonas. The thylakoids purified from wild type contained 40% of total FNR and showed NADP photoreduction activity in the presence of ferredoxin. In contrast, the thylakoids isolated from photosystem I mutant lacked FNR. These results suggest that the association of FNR with the thylakoids is stabilized by the presence of photosystem I complex. However, the absence of cytochrome b6f and photosytem II also affected the stability of FNR on the thylakoids. We will discuss a possible function of the bound FNR.
