[Reduction of cytochrome c by NADH induced by light]

We have studied the behaviour of Fe(III) cytochrome c upon irradiation in the 290-360 nm wavelength range either in the presence or in the absence of NADH; in both cases the photoexcitation caused the reduction of the heme iron. When the irradiation was performed in the absence of NADH, the iron reduction was coupled to a non reversible modification in the protein structure; the photoreduction quantum yield was decreasing with the increase of the irradiation wavelength. Irradiation in the presence of NADH gave heme iron reduction coupled to NADH oxidation and the protein resulted finally unmodified; the quantum yield depended on the irradiation wavelength in a way similar to the observed in the absence of NADH, but it was tenfold higher. We propose that in both cases the active species is an electronic excited state of the heme iron.