ω-1, ω-2 and ω-3 Hydroxylation of long-chain fatty acids, amides and alcohols by a soluble enzyme system from Bacillus megatyerium

Abstract

A soluble enzyme preparation from Bacillus megaterium, previously shown to hydroxylate free fatty acids to isomeric mixtures of ω-1, ω-2 and ω-3 monohydroxy fatty acids in the presence of NADPH and O 2, has now been shown to act also on fatty alcohols and fatty amides but not on hydrocarbons or fatty acid methyl esters. Using 14C-labelled substrates, both the chainlength specificity and the positional specificity of hydroxylation was determined for fatty acids, alcohols and amides. The most active saturated fatty acid (pentadecanoic) was hydroxylated at a rate 10 times greater than the most active amide (myristamide) and 14 times faster than the most active alcohol (1-tetradecanol). Among the saturated fatty acids, the order of activity as hydroxylation substrates was C 15 > C 16 > C 14 > C 17 > C 13 > C 18 = C 12. For amides the order was C 14 > C 12 > C 15 > C 16 while for alcohols it was C 14 > C 13 = C 15 > C 12 > C 16. Four cis-monounsaturated fatty acids were also tested. Oleic, palmitoleic and cis-12-octadecenoic acids were more active than their saturated analogs but cis-5-tetradecenoate was less active than myristate. For all of the substrates mentioned above, with the possible exception of several unsaturated acids, the alkyi chains were monohydroxylated to give isomeric mixtures of the ω-1, ω-2 and ω-3 derivatives. The distribution of these three isomers varied with chain-length and type of substrate but generally, the ω-2 position was favored. The terminal methyl (ω) group of these substrates was never hydroxylated and there did not appear to be significant hydroxylation of methylene carbons beyond the ω-3 position. Based on the data presented here and in a previous paper, a model is proposed for the enzyme-substrate complex which involves hydrophobic binding and sequestering of the terminal methyl group of the substrate and electrostatic binding of the substrate's polar functional group.