Abstract
Pyridine nucleotide transhydrogenase was extracted from mitochondria of yellowtail muscle prefrozen below -20°C. The extract was applied to DEAE-cellulose column chro-matography, resulting in the appearance of two isozymes. The first peak named isozyme-I exhibited both T. D and D. D activities, whereas the second peak named isozyme-II exhibited only D. D activity. Both isozymes were highly purified by repetition of Sephadex G-200 gel filtration and DEAE-cellulose column chromatography. The specific activities of isozyme-I preparation thus obtained were about 500 (T. D) and 140 (D. D) times as high as those of the extract. The specific activity of the isozyme-II preparation was about 600 times in respect of D. D activity. Molecular weights of isozyme-I and -II were estimated at about 37, 000 and 48, 000 respectively by SDS-disc electrophoresis. Absorption spectra of both isozymes showed a maximum at 280nm. Neither of them, however, exhibited any flavin specific maximum around 442nm. This seems to indicate that neither of the yellowtail enzymes are flavopro-teins, unlike the enzymes of bacterial origin.
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