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) 3 complex at the surface‐exposed cysteine residues, 62 and 387. The laser‐flash/quench technique was used to study Ru 1+ → Fe 3+ electron transfer (ET) within the Ru‐BMP complexes. There was no reduction of the ferric heme by Ru 1+ in Ru‐62‐BMP. In Ru‐387‐BMP, ET from Ru 1+ to Fe 3+ occurred with the rate constant of 4.6 × 10 5 s −1 and 2.5 × 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.