COMPARISON OF METABOLIC FLUXES OF CIS-5-ENOYL-COA AND SATURATED ACYL-COA THROUGH THE BETA-OXIDATION PATHWAY

The metabolic fluxes of cis-5-enoyl-CoAs through the beta-oxidation cy cle were studied in solubilized rat liver mitochondrial samples and co mpared with saturated acyl-CoAs of equal chain length. These studies w ere accomplished using either spectrophotometric assay of enzyme activ ities and/or the analysis of metabolites and precursors using a gas ch romatographic method after conversion of CoA esters into their free ac ids. Cis-5-enoyl-CoAs were dehydrogenated by acyl-CoA oxidase or acyl- CoA dehydrogenases at significantly lower rates (10-44 %) than saturat ed acyl-CoAs. However, enoyl-CoA hydratase hydrated trans-2-cis-5-enoy l-CoA at a faster rate (at least 1.5-fold) than trans-2-enoyl-CoA. The combined activities of 3-hydroxyacyl-CoA. dehydrogenase and 3-keto ac yl-CoA thiolase for 3-hydroxy-cis-5-enoyl-CoAs derived from cis-5-enoy l-CoAs were less than 40 % of the activity for the corresponding 3-hyd roxyacyl-CoAs prepared from saturated acyl-CoAs. Rat liver mitochondri al beta-oxidation enzymes were capable of metabolizing cis-5-enoyl-CoA via one cycle of beta-oxidation to cis-3-enoyl-CoA with two less carb ons. However, the overall rates of one cycle of beta-oxidation, as det ermined with stable-isotope-labelled tracer, was only 15-25 %, for cis -5-enoyl-CoA, of that for saturated acyl-CoA. In the presence of NADPH , the metabolism of cis-5-enoyl-CoAs was switched to the reduction pat hway. Therefore, in intact liver mitochondria, where the NADPH/NADP(+) and NAD(+)/NADH ratios are high, the predominant pathway for the meta bolism of cis-5-enoyl-CoAs could be reduction via 2,4-dienoyl-CoA redu ctase after isomerization of Delta 3 Delta 5-dienoyl-CoA to trans-2-tr ans-4-dienoyl-CoA.