魚類筋肉のpyridine nucleotide transhydrogenaseに関する研究-3-酵素化学的性質とKinetics〔英文〕

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Enzymatic properties of the two isozymes (I and II) of yellowtail pyridine nucleotide transhydrogenase were examined. Isozyme-I showed a pH optimum at 7.8 in respect of T.D activity, and two optima at 6.5 and 7.8 in respect of D. D activity. Isozyme-II exhibiting only D. D activity showed a pH optimum at 6.5. Neither isozyme was activated by 2'-AMP, which activates Pseudomonas transhydrogenase. Some nucleotides and lecithin which affect in various ways the enzymes from other sources did not show any effect on the activity of isozyme-II. In addition, calcium chloride enhanced effectively the activity of isozyme-II. On the contrary, the activity was to some extent inhibited by manganese and cupric chloride. Kinetic constants, KTNAD, KNADH2, and V1, were 13 μM, 12 μM, and 9.1 μmole-min-1. mg protein-1, respectively. Based on the results of kinetic studies, the reaction mechanism of isozyme-II was classified from among various mechanisms proposed by CLELAND as a Theorell-Chance mechanism.