Electrocatalytic Investigation of Light-Induced Electron Transfer between Cytochrome c&[SUB2] and Photosystem I.

A light-activated electron-transfer chain was assembled using solubilized cyanobacterialphotosystem I as photoactive enzyme, cytochrome 06 (also from cyanobacteria) as electron donor, andmethyl viologen as electron acceptor. The photocatalytic activity of the ensemble was measured by directand reversible electrochemistry of cytochrome 06 at a surface-modified gold electrode. Analysis of theelectrochemical 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. [ABSTRACT FROM AUTHOR]