Electron transfer in the ruthenated heme domain of cytochrome P450BM-3

Two mutants of the heme domain of Bacillus megaterium cytochrome P450BM-3 (BMP) have been modified by covalent attachment of a photoactive Ru(bpy), complex at the surface-exposed cysteine residues, 62 and 387. The laser-flash/quench technique was used to study Ru1+ --> Fe3+ electron transfer (ET) within the Ru-BMP complexes. There was no reduction of the ferric heme by Ru1+ in Ru-62-BMP. In Ru-387-BMP, ET from Ru1+ to Fe3+ occurred with the rate constant of 4.6 x 10(5) s(-1) and 2.5 x 10(6) s(-1) in the absence and presence of substrate, respectively. The study demonstrates the importance of through-bond pathways for electron flow to the heme iron of P450 and that the Gln(387)-Cys(400) peptide is a potential ET root in P450BM-3.