魚類の脂肪酸代謝に関する研究(I) : コイ肝膵臓ミトコンドリアによる脂肪酸のβ-酸化

Abstract

It has been known that lipids play as energy source, cushion, insulation, etc. In fact, there are many reports that lipids are effective as a energy source in feeding experiments on fish as well as on land animals, and a lipid supplement to dietary was recently carried out in cultivating fish. However, there are almost no reports discussing the efficiency of lipids in dietary from the viewpoint of enzyme chemistry. The present paper is concerned with occurrence and some of properties of β-oxidation system in carp (Cyprinus carpio) hepatopancreas mitochondria, aiming at the utilization of lipids by fish. The occurrence of β-oxidation system in carp hepatopancreas mitochondria was confirmed by the following evidences: O_2 uptake and subsequent decrease of substrate, octanoate, based on β-oxidation, effects of ATP, Mg^++ and cytochrome c as cofactors on O_2 uptake, and no O_2 uptake in the mitochondria after heat treatment. The optimum pH of this enzymatic system was 7.8 and the optimum temperature was 25℃, with octanoate as a substrate. Effect of α-ketoglutarate, a TCA cycle intermediate, on β-oxidation system was clearly different from those of ATP, Mg^++ and cytochrome c, and α-ketoglutarate was recognized as a sparker in β-oxidation. Endogenous respiration and β-oxidation systems were inhibited by malonate and α-dinitrophenol, and there were some differences in their inhibition rates. Therefore it could be presumed that malonate and α-dinitrophenol inhibited β-oxidation according to the different mechanisms.