omega- and (omega--1)-hydroxylation of fatty acids by frog liver microsomes. Substrate specificity and other properties.

Frog liver microsomes catalyzed the hydroxylation of various saturated fatty acids whose chain lengths were from 8 to 18 carbon atoms into the corresponding omega- and (omega--1)-hydroxy derivatives. In addition, small amounts of the dicarboxylic acids and (omega--1)-keto acids were also formed from all the fatty acids. The relative activity of the hydroxylase with the substrates was as follows: C13(100), C12(98), C14(88), C10(62), C16(34), C18(29), and C8(8). The percentage of omega-hydroxy derivative relative to the (omega--1)-isomer increased with increasing carbon chain length of the fatty acid substrate. Oleate, linoleate and linolenate were also tested and found to be at least as active their saturated analog (stearate). Both NADPH and O2 were required for hydroxylase activity. The apparent Km for NADPH was 3.7 . 10(-5) M, and NADH had very little effect. The apparent Km value for laurate was 1.5 . 10(-5) M. The hydroxylating system was about 50% inhibited by 10 mM KCN and 81% inhibited by CO at a CO : O2 ratio of 4.0. In contrast, NaN3 showed no effect on hydroxylation.