β-Oxidation of the geometric and positional isomers of octadecenoic acid by rat heart and liver mitochondria

Abstract

The cis and trans isomers of Δ 4 through Δ 16 octadecenoic acid, all present in partially hydrogenated soybean oil, were compared as substrates for β-oxidation by isolated rat heart and liver mitochondria. The fatty acids were converted to their coenzyme A esters and oxygen uptake rates measured polarographically in the presence of l-malate, l-carnitine, ADP, and optimum albumin. The cis isomers were catabolized in a similar pattern by heart and liver. The even-positioned cis isomers were oxidized significantly more slowly than adjacent odd-positioned isomers. Most odd-positioned cis isomers were oxidized as rapidly as oleoyl-CoA. The pattern of catabolism of the trans isomers, however, was different from the cis isomers. Liver mitochondria oxidized most even-positioned trans isomers significantly more rapidly than adjacent odd-positioned isomers. The same pattern was observed with heart mitochondria only for the trans isomers in which the double bond was located near the middle of the acyl chain. Heart mitochondria oxidized nearly all the trans isomers significantly more slowly than stearoyl-CoA; however, liver mitochondria oxidized the even-positioned trans isomers nearly as rapidly as stearoyl-CoA. Both heart and liver mitochondria oxidized the cis isomers, especially Δ 9 and Δ 11, significantly more rapidly than their respective trans isomers, with three notable exceptions: Δ 8, Δ 10, and Δ 14. 3-Hydroxyacyl-CoA epimerase and Δ 3- cis- Δ 2- trans-enoyl-CoA isomerase account for most of the observed β-oxidation patterns. An additional and more efficient pathway for the β-oxidation of n-6 fatty acids is suggested.