Light-induced oxidation of cytochrome c

Abstract

Photooxidation of pyranine (8-hydroxypyrene-1,3,6-trisulfonate) by an intensive UV laser pulse (20-60 MW/cm2) leads to an instantaneous formation of the oxidized form of the dye. The redox reaction between the oxidized dye and ferrocytochrome c was followed by transient absorption spectroscopy looking either at re-reduction of oxidized pyranine or the oxidation of the cytochrome. At high ionic strength (100 mM Hepes and 20 mM KCI, pH 6.5), second-order kinetics of ferrocytochrome-c oxidation was observed with a rate constant of (3.2 ± 0.3) · 109 M-1s-1. At lower ionic strength a 1:1 complex was formed between the cytochrome and pyranine. The rate for intracomplex electron transfer was found to be (3.6 ± 0.2) · 106 s-1. This rapid photooxidation of cytochrome c makes it a useful tool for fast initiation of a synchronized electron flow within redox proteins. © 1995.