Structural similarities and differences of the heme pockets of various P450 isoforms as revealed by resonance Raman spectroscopy

Cytochromes P450 CYP102 Al, 1A2, and 3A4, all belonging to the class II typ e of P450 enzymes, were studied by resonance Raman spectroscopy. Spectra we re measured for the oxidized substrate-free, oxidized substrate-bound, and reduced forms of each of these P450s. The analysis of the resonance Raman s pectra indicates that the individual isoforms differ with respect to orient ation and conformations of the heme side chains, whereas the overall porphy rin geometry is essentially the same. In the oxidized state, the vinyl grou ps exhibit both a coplanar and an out-of-plane orientation with respect to the heme, albeit with different relative propensities in the various isofor ms. In the reduced state, both vinyl groups are forced into a coplanar orie ntation. In addition to the differences in behavior of the vinyl groups, th e redox-linked spectral changes also include the bending mode of the propio nate side chains. The spectral differences associated with the porphyrin su bstituents are likely to reflect subtle conformational differences in the h eme pocket of various P450 isoforms which may constitute the structural bas is for the known variability of their functions, (C) 2000 Academic Press.