FATTY ACID-INDUCED ALTERATION OF THE PORPHYRIN MACROCYCLE OF CYTOCHROME-P450 BM3

Surface-enhanced resonance Raman scattering (SERRS) of substrate-free and substrate-bound forms of the P450 domain of cytochrome P450 BM3 ar e reported and assigned. Substrate-free P450 yields mixed spin heme sp ecies in which the pentacoordinate high-spin arrangement is dominant. The addition of laurate or palmitate leads to an increase in high spin content and to an allosteric activation of heme mode v(29), which is sensitive to peripheral heme/protein interactions. Differences between laurate and palmitate binding are observed in the relative intensitie s of a number of bands and the splitting of the heme vinyl modes. Laur ate binding to P450 results in different protein environments being ex perienced by each vinyl mode, whereas palmitate binding produces a sma ller difference. The results demonstrate the ability of SERRS to probe substrate/prosthetic group interactions within an active site, at low protein concentrations.