PEROXISOMAL BETA-OXIDATION IS A SIGNIFICANT PATHWAY FOR CATABOLISM OFFATTY-ACIDS IN A MARINE TELEOST

Hepatic beta-oxidation is characterized in a marine teleost, Myoxoceph alus octodecimspinosus, to determine mitochondrial and peroxisomal sub strate selectivity as well as metabolic partitioning. Substrate select ivity is broad for peroxisomal beta-oxidation. Acyl CoA oxidase activi ties, with all unsaturated substrates measured, are at least 35% of ac tivity with palmitoyl CoA (16:0), a saturated substrate. Mitochondrial selectivities are more pronounced. Carnitine palmitoyltransferase act ivity with a monounsaturate, palmitoleoyl CoA (16:1), is nearly 40% gr eater than activity with palmitoyl CoA, whereas activities with two po lyunsaturates are <10% of activity with the saturate. The presence of polyunsaturated acyl CoA esters inhibits up to 70% the oxidation of pa lmitoyl CoA by intact peroxisomes. Acyl CoA hydrolase activity is loca lized to peroxisomal fractions prepared by density-gradient centrifuga tion. Hydrolytic activity in these fractions is nearly twofold the act ivity of beta-oxidation. Estimates for metabolic partitioning suggest that at least 50% of hepatic beta-oxidation may be initiated by the pe roxisomal compartment.