The FB iron-sulfur cluster is destroyed preferentially by treating Photosystem I complexes with HgCl2(Kojima Y, Niinomi Y, Tsuboi S, Hiyama T and Sakurai H (1987) Bot Mag 100: 243-53). When FB is 95% depleted but FAis quantitatively retained in cyanobacterial PS I complexes, the reduction potential of FA remains highly electronegative (Em=-530 mV, n=1), the EPR spectral and spin relaxation properties of FA and FXremain unchanged, but NADP+ photoreduction rates decline from 552 to 72 μmol mg Chl-1 h-1.When FB is reconstituted with FeCl3, Na2S and β-mercaptoethanol, NADP+photoreduction rates recover to 528 μmol mg Chl-1 h-1. The correlation between the presence of FBand NADP+ photoreduction provides direct experimental evidence that this iron-sulfur cluster is required for electron throughput from cytochrome c6 to flavodoxin or ferredoxin in Photosystem I.
All Science Journal Classification (ASJC) codes
- Plant Science
- Cell Biology