Reduction of photosystem I by cytochrome c6 and plastocyanin: molecular recognition and reaction mechanism

Abstract

Molecular recognition and protein-protein electron transfer reactions were studied in a model system in which two structurally different proteins (cytochrome c 6 and plastocyanin) are used alternatively to accomplish the same redox event, i.e. reduction of the photo-oxidized chlorophyll molecule P700 − in photosystem I (PSI). Laser flash photolysis kinetic analyses were carried out to obtain an understanding, from a structural and functional point of view, of how this interchange ability is accomplished, as well as to obtain increased insight into the electron transfer mechanisms. Our experimental data indicate that the mechanism of reaction of both the copper-and heme-proteins with PSI is similar within the same organism, but different from one organism to another, thereby suggesting convergent evolution of the two donor proteins.