Substrate selectivities differ for hepatic mitochondrial and peroxisomal β-oxidation in an Antarctic fish, Notothenia gibberifrons

Abstract

Hepatic mitochondrial and peroxisomal β-oxidation were examined in an Antarctic marine teleost, Notothenia gibberifrons. Enzymic profiles and rates of β-oxidation by intact organelles were determined by using a range of fatty acyl-CoA substrates to evaluate substrate preferences. Partitioning of β-oxidation between organelles was estimated. Substrate selectivities are broader for peroxisomal β-oxidation than for mitochondrial β-oxidation. Mitochondria show marked preference for the oxidation of a monounsaturated substrate, palmitoleoyl-CoA (C16.1) and two polyunsaturates, eicosapentaenoyl-CoA (C20.6) and docosahexaenoyl-CoA (C22.6). Carnitine palmitoyltransferase activities with palmitoleoyl-CoA (C16.1) are 2.4-fold higher than activities with palmitoyl-CoA (C16.0). Most polyunsaturated acyl-CoA esters measured appear to inhibit by over 40% the oxidation of palmitoyl-CoA by peroxisomes. Our findings suggest that the polyunsaturates, eicosapentaenoic acid (C20.5) and docosahexaenoic acid (C22.6), found in high concentrations in Antarctic fishes [Lund and Sidell (1992) Mar. Biol. 112, 377-382], are utilized as fuels to support aerobic energy metabolism. Metabolic capacities of rate-limiting enzymes and β-oxidation rates by intact organelles indicate that up to 30% of hepatic β-oxidation in N. gibberifrons can be initiated by the peroxisomal pathway.