Cytochrome P-450 enzymes (EC 1.14.14.1, nonspecific monooxygenase)
catalyze the oxidations of many chemicals (1). The
mass of the substrates ranges from that of ethylene (Mr 28) to
that of cyclosporin A (M, 1201). The classification of a hemoprotein
asa P-450’ is defined by its absorption spectrum; thFee (I1)-
CO complex has a characteristic absorption maximum (Soret
band) near 450 nm due to axial ligation with a cysteine thiolate
of the protein (with or without substrate present). This cysteine
residue is present in a relatively well conserved region, -80% into
the protein from the N terminus. Collectively there are thousands
of potential substrates for the P-450s; each of the P-450s may
have a rather strict limitation of catalytic specificity (e.g. P-450s
involved in steroid anabolism) or be a catalyst for the oxidation
of many substrates (e.g. some of the inducible P-450s utilized in
xenobiotic oxidation). There are many different P-450e nzymes;
we now realize that there can be >30 P-450 (or so-called “CY,”)
genes expressing their products in a single organism, and many
of these are concurrentlyp roduced in a single tissue.T hese genes
have been classified on the basiso f their coding sequences (2