Electron Transfer between Plastocyanin and P700 in Various Types of Photosystem I Complex1

Three types of PS I Chl-protein complex, PS I 180, PS I 65, and PS I 30, have been prepared and the kinetic properties of the transfer of electrons from plastocyanin to P700 in the PS I complexes with different sized antennae were examined. The PS I 180 complex, which consists of 180 Chi per P700, showed the almost same rate constant and effects of cations for the transfer of electrons from plastocyanin to P700 as those obtained with PS I-enriched membrane fragments. The rate constant increased with the addition of low concentrations of monovalent and divalent cations, but decreased with high concentrations of cations. However, the rate was severely reduced in the case of the PS I 65 and PS I 30 complexes, and quite different effects of cations were observed. Given the presence of additional 25- to 28-kDa polypeptides in the PS I 180 complex as compared to the PS I 65 and PS I 30 complexes, we discuss a possible function for these polypeptides in the regulation of the reaction between plastocyanin and P700.