Catalytic properties of rabbit kidney fatty acid ω-hydroxylase cytochrome P-450ka2 (CYP4A7)

Abstract

We have examined in detail the substrate specificity of a rabbit kidney fatty acid ω-hydroxylase, designated cytochrome P-450ka2 (CYP4A7). The hydroxylation products were identified as ω- and (ω - 1)-hydroxy fatty acids mainly using gas chromatography-electron impact mass spectrometry. [1]Straight-chain saturated fatty acids ranging from 10 to 19 carbons were effectively hydroxylated at the ω- and (ω - 1)-position. The ratios of ω- to (ω - 1)-hydroxylation activity decreased with increasing the carbon chain length of fatty acids. [2]Both isomyristate and anteisomyristate, and isopalmitate were hydroxylated several fold more rapidly than myristate and palmitate, respectively, with iso-branched chain fatty acids being hydroxylated at the ω-position solely. [3]Both palmitoleate and palmitoelaidate, and both oleate and elaidate were hydroxylated much more rapidly than palmitate and stearate, respectively. [4]Linoleate, γ-linolenate, and arachidonate were also excellent substrates for this enzyme. [5]Prostaglandin (PG) A 1 and PGA 2 were efficiently hydroxylated at the ω-position solely, with PGE 1 and PGE 2 being much less active. [6]Arachidonic acid not only showed a K m value significantly lower than those for lauric acid, γ-linolenic acid and PGA 1, but also it is a potent competitor for lauric acid and PGA 1, showing a very high affinity for the enzyme. It is possible that arachidonic acid is the physiological substrate for kidney P-450ka2.