Fig. 1 (IMAGE) Osaka University Caption The proposed mechanism underlying the function of cyanobacterial PSI. Upon binding of Fd, the vertical piston-like motion of PsaF may serve to couple sequential electron transfer from Cyt c6 to the PSI protomers in turn. Credit Osaka University Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.