HETEROATOM SUBSTITUTION SHIFTS REGIOSELECTIVITY OF LAURIC ACID METABOLISM FROM OMEGA-HYDROXYLATION TO (OMEGA-1)-OXIDATION

In contrast to several isofoms of cytochrome P450 (including 1A1, 1A2, 2B1, 2C2, 2C6 and 2E1), cytochrome P450 4A1 and a fusion protein derived from it, show a strong preference for hydroxylation of lauric acid (C-12) at the less chemically reactive omega-CH3 group instead of the more reactive (omega-1)-CH2 group. We have explored the interplay of steric effects on substrate binding vs chemical reactivity at various substrate loci in determining the striking difference in regioselectivity of CYP2B1 and a 4A1-derived fusion protein, through studies with heteroatom substituted analogs of lauric acid, i.e.,10-methoxydecanoic acid and 10-methylthiodecanoic acid. With both enzymes the former undergoes simple omega-hydroxylation (giving 10-hydroxydecanoic acid and HCHO), but the latter undergoes facile S-oxidation at the omega-1 position instead of omega-hydroxylation. The dramatic shift in the regioselectivity of the fusion protein toward the thia analog is consistent with the greater length of C-S bonds and the greater atomic radius and polarizability of sulfur lone-pair electrons within an otherwise restrictive active site. (C) 1995 Academic Press, Inc.