Direct hydroxylation of primary carbons in small alkanes by wild-type cytochrome P450BM3 containing perfluorocarboxylic acids as decoy molecules

Abstract

Cytochrome P450BM3 (P450BM3) is a long-alkyl-chain fatty acid hydroxylase that shows an extremely high catalytic turnover rate and high coupling efficiency of NADPH for product formation (product formation rate per NADPH consumption rate). Although P450BM3 exclusively hydroxylates long-alkyl-chain fatty acids, we have found that simple addition of perfluorocarboxylic acids (PFs) as inert dummy substrates (decoy molecules) turns P450BM3 into a small alkane hydroxylase. For example, PF-bound P450BM3 oxidizes propane and butane to 2-propanol and 2-butanol, respectively. The coupling efficiency of small alkane hydroxylation, however, is very low compared with that of long-alkyl-chain fatty acid hydroxylation. In this study, we examined the experimental conditions for small alkane hydroxylation in an effort to improve the coupling efficiency and to realize the hydroxylation of their primary carbons. To increase the concentration of gaseous substrates in the reaction mixture, we performed reactions under the high-pressure condition of 0.5 MPa small alkanes. Propane hydroxylation under high-pressure conditions significantly improved the coupling efficiency to 48%. Furthermore, 1-propanol, which has never been observed under lower-pressure conditions, was produced. It is noteworthy that a detectable amount of ethanol was observed in the ethane hydroxylation under the pressure condition of 0.5 MPa, whereas methane was not hydroxylated. These results indicate that by increasing the concentration of small alkanes, the “P450BM3–decoy molecule system” can catalyze hydroxylation reactions of the primary carbons in small alkanes.