POSITIONAL SPECIFICITY OF RABBIT CYP4B1 FOR OMEGA-HYDROXYLATION OF SHORT-MEDIUM CHAIN FATTY-ACIDS AND HYDROCARBONS

Rabbit CYP4B1 was incubated with a series of fatty acid and hydrocarbo n substrates and metabolites were identified by gas chromatography and gas chromatography/mass spectrometry. C-7 to C-10 n-alkyl fatty acids were preferentially hydroxylated at the terminal carbon (omega/omega- 1 = 1.1-7.4) with turnover numbers of 1-11 min(-1). The C-7 to C-10 n- alkyl hydrocarbons exhibited turnover numbers of 11-33 min(-1) for the corresponding reactions and even higher regioselectivities for hydrox ylation at the thermodynamically disfavored site (omega/omega-1 = 1.6- 23). These results demonstrate a functional link between CYP4B1 and ot her CYP4 fatty acid hydroxylases, and show further that CYP4B1's unusu al positional specificity is not dictated by the presence of a carboxy late (or polar) anchor on the substrate. This suggests the presence of a dominant hydrocarbon binding site which effectively restricts the a ccess of short-medium chain n-alkyl substrates to the perferryl specie s in the active site of rabbit CYP4B1. (C) 1998 Academic Press.