Picking on someone smaller. Cytochromes P450 catalyze the hydroxylation of thousands of substrates, including alkanes. No naturally occurring P450, however, is known to oxidize the smallest alkanes, ethane and methane. Here we report the direct and selective oxidation of ethane to ethanol using dioxygen, catalyzed by a cytochrome P450 BM‐3 variant engineered for high activity towards small alkanes (see scheme). Achieving P450‐catalyzed oxidation of ethane is a key step in the pathway to P450‐catalyzed methane oxidation and opens new opportunities for the bioconversion of natural gas to fuels and chemicals.

Here we demonstrate that a small panel of variants of cytochrome P450 BM3 from Bacillus megaterium covers the breadth of reactivity of human P450s by producing 12 of 13 mammalian metabolites for two marketed drugs, verapamil and astemizole, and one research compound. The most active enzymes support preparation of individual metabolites for preclinical bioactivity and toxicology evaluations. Underscoring their potential utility in drug lead diversification, engineered P450 BM3 variants also produce novel metabolites by catalyzing reactions at carbon centers beyond those targeted by animal and human P450s. Production of a specific metabolite can be improved by directed evolution of the enzyme catalyst. Some variants are more active on the more hydrophobic parent drug than on its metabolites, which limits production of multiply-hydroxylated species, a preference that appears to depend on the evolutionary history of the P450 variant.