スジイルカ筋肉におけるmetmyoglobin還元酵素系に関する研究-3-Ferrimyoglobin redactaseのアミノ酸組成および酵素化学的性質〔英文〕

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Amino acid composition and enzymatic properties of dolphin ferrimyoglobin reductase (Fer-riMb R) were studied and compared with those of the ferrihemoglobin reductase (Fer-riHb R) from the same source. There was a general resemblance between their amino acid compositions, although slight but clear differences were recognized in contents of several amino acids such as Asp, Leu, Tyr, and Arg. Both reductases also differed from each other in the number of easily reactive sulfhydryl groups as well as in the number of disulfide bonds. With either reductase, NADH2 was found to serve much more effectively as an electron donor than NADPH2. Both enzymes showed comparable specific activities in reduction of ferric hemoproteins. The optimum pH values of FerriHb R were 5.4 and 5.3 for metmyoglobin (MMb) and methemoglobin (MHb), respectively, and those of FerriMb R were both 5.0. The activities of FerriHb R and FerriMb R reached the maximum at 30°C and 25°C, respectively. Menadione exhibited some accelerating effect on the reduction of ferric hemoproteins by either reductase. Michaelis constants for FerriHb R were 1.1, 1.4, and 1.2x10-4M for MMb, MHb, and FerriCyt. c, respectively, while those for FerriMb R 3.3, 4.1, and 1.2x10-4M, respectively. The MMb reducing activity of FerriMb R was strongly inhibited by sulfhydryl reagents.
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