抄録
Changes in the metabolic pathways of hypoxanthine in a strain of Streptomyces sp. has been studied. Hypoxanthine was converted to inosine 5′-monophosphate by the cells of the early period of cultivation, in which a high activity of hypoxanthine phosphoribosyltransferase but none of xanthine dehydrogenase was found, and was oxidized to xanthine and 6, 8-dihydroxypurine by those of the middle and the late periods, in which both activities were observed. If the cells of the early growth period were starved of the nitrogen source, the activity of xanthine dehydrogenase increased and hypoxanthine stimulated the increase, whereas that of hypoxanthine phosphoribosyltransferase remained constant. Synthesis of the nucleotide but not the oxidation was inhibited under these conditions of nitrogen limitation. If the cells were then supplied with the nitrogen source, however, the purine base was metabolized to both the synthetic and oxidative directions at the same time. These results suggest that the nitrogen source in the medium plays an important role in the control of hypoxanthine metabolism; repressing the formation of xanthine dehydrogenase on the one hand and promoting the reaction of hypoxanthine phosphoribosyltransferase on the other.
