CHANGES IN THE METABOLIC PATHWAYS OF HYPOXANTHINE IN STREPTOMYCES

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Abstract
Changes in the metabolic pathways of hypoxanthine in a strain of Streptomyces sp. were studied. Hypoxanthine was converted to IMP 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 N 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 N limitation. If the cells were then supplied with the N source, the purine base was metabolized to both the synthetic and oxidative directions at the same time. The N source in the medium apparently plays an important role in the control of hypoxanthine metabolism: repressing the formation of xanthine dehydrogenase and promoting the reaction of hypoxanthine phosphoribosyltransferase.