A mechanism of direct photoreduction of ferricytochrome c.

Abstract

A mechanism of direct photoreduction of ferricytochrome c was investigated by using continuous UV-irradiation and flash photolysis. The photoreduction was found to follow a biphotonic process and to be considerably suppressed by nitrous oxide and oxygen. The fact that urea caused an increase in the rate of photoreduction suggests that the close contact of tryptophyl residue with the heme was lost. Participation of tryptophyl residue was confirmed by the efficiency of aromatic amino acids on indirect photoreduction and a transient absorption with a peak at about 530 nm in the presence of urea. The quantum yield of the photoionization was estimated to be (3.9 ± 0.3)×10-3. A mechanism is proposed that the hydrated electrons produced by the photoionization of aromatic amino acid residue(s), tryptophyl and tyrosyl, take part in the photoreduction of ferricytochrome c.