魚類糖代謝の調節―ＸＸＶＩＩＩ 数種飼料条件に対する魚類肝臓のＮＡＤ‐およびＮＡＤＰ‐イソクエン酸脱水素酵素活性の応答

Abstract

Responses of hepatic NAD-and NADP-isocitrate dehydrogenase (NAD-and NADP-ICD) activities to dietary composition and feeding rates were examined in carp Cyprinus carpio and tilapia Oreochromis niloticus. Soluble NADP-ICD activity was relatively high in fish fed high carbohydrate diets and in those fed at high feeding rates probably causing an active lipogenesis. On the other hand, the activity was relatively low in starved fish and in those fed high lipid diets probably causing an inactive lipogenesis. This result together with the previous study on the enzyme distribution in fish tissues and hepatic cells suggest that the soluble enzyme of fish liver contributes to fatty acid biosynthesis through the supply of NADPH produced by the enzyme reaction. On the other hand, mitochondrial NAD-ICD activity remained practically constant, independent of the different dietary conditions. although its activity decreased slowly during prolonged starvation. This may indicate that the mitochondria enzyme contributes to the production of ATP through the supplementation of NADH to electron transport system.