Abstract
A pyridine nucleotide transhydrogenase activity, supported by ATP or by succinate oxidation, was demonstrated in phosphorylating membrane fragments from Micrococcus denitrificans. The ATP-supported reaction was inhibited by various energy-transfer inhibitors and uncouplers or by treatment with high concentrations of LiCl. P i and arsenate showed a stimulatory effect on the ATP-supported activity; half-maximal stimulation was attained by about 80 μM phosphate. The transhydrogenase reaction dependent on succinate oxidation was not appreciably inhibited by energy-transfer inhibitors, although oleate and pentachlorophenol were almost equally effective in both reactions. P i did not stimulate the succinate-supported activity. From the effects of thyroxine and its derivatives on the energy-dependent and independent reductions of NAD + by NADPH, the involvement of the same transhydrogenase enzyme in both reactions was suggested. These and other results indicated that the energy-transfer system of M. denitrificans was very similar to, though not identical with, that of mammalian mitochondria.
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