Kinetic studies on the oxidation of cytochrome b5 Phe35 mutants with cytochrome c, plastocyanin and inorganic complexes

To illustrate the functions of the aromatic residue Phe35 of cytochrome b5 and to give further insight into the roles of the Phe35-containing hydrophobic patch and/or aromatic channel of cytochrome b5, we studied electron transfer reactions of cytochrome b5 and its Phe35Tyr and Phe35Leu variants with cytochrome c, with the wild-type and Tyr83Phe and Tyr83Leu variants of plastocyanin, and with the inorganic complexes [Fe(EDTA)]–, [Fe(CDTA)]– and [Ru(NH3)6]3+. The changes at Phe35 of cytochrome b5 and Tyr83 of plastocyanin do not affect the second-order rate constants for the electron transfer reactions. These results show that the invariant aromatic residues and aromatic patch/channel are not essential for electron transfer in these systems.