Electrocatalytic investigation of light-induced electron transfer between cytochrome c6 and photosystem I.

A light-activated electron-transfer chain was assembled using solubilized cyanobacterial photosystem I as photoactive enzyme, cytochrome c(6) (also from cyanobacteria) as electron donor, and methyl viologen as electron acceptor. The photocatalytic activity of the ensemble was measured by direct and reversible electrochemistry of cytochrome c(6) at a surface-modified gold electrode. Analysis of the electrochemical response with an appropriate model for the reaction mechanism allowed the relation of the overall catalytic reaction rate to the individual steps of the catalytic cycle. Second-order rate constants were determined for the first time under steady-state conditions. The results validate this approach as an efficient method for the study of electron transfer between photoactive enzymes and their redox partners.