Thiol-containing peptide-hemin complexes as models of cytochrome P-450

Nine different synthesized thiol tetra- and penta-peptides containing Cys-Ser, Cys-Thr, Cys-His, Cys-Tyr and Cys-Cys in the N- and C-terminals are proposed as new models of apo-P-450. The peptide-hemin complexes in the oxidized (Fe(III] form in solution were characterized by their optical and EPR spectra and found to show hydroxylation activity like that of P-450 enzymes on acetanilide. Although the EPR properties of the complex containing Cys-His and all complexes in the presence of pyridine were similar to those of P-450, the optical properties of these complexes were not completely similar to those of P-450. Based on these results, the sixth heme coordination site of P-450 was discussed.