Activation of long chain fatty acids by subcellular fractions of rat liver: III. Effect of ethylenic bond position on acyl-CoA formation ofcis-octadecenoates

Abstract

The rates of rat liver microsomal and mitochondrial activation of the Δ⁴ to Δ¹⁷ cis-octadecenoate positional isomers have been investigated. The fatty acid to protein ratios required for maximum activation of the Δ⁸, Δ⁹ and Δ¹⁰ isomers were much lower than the corresponding ratios required for maximum activation of thecis-octadecenoates with double bonds at either end of the fatty acid molecule. Also, as the incubation temperature was raised from 22–38 C the Δ⁸ and Δ⁹ isomers exhibited little change in their rates of activation, while large increases in activation rates of the isomers with the double bond at either end of the fatty acid chain were observed. Differential inhibition of the activation of the various positional isomers was observed when anionic, cationic, or nonionic detergents were included in the incubation medium. The different responses to fatty acid concentration, temperature and detergents are attributed to enzyme specificity and to differences in solution properties of thecis-octadecenoates, rather than to the presence of separate rat liver enzymes that catalyze acyl-CoA ester formation of the various positional isomers.