抄録
The regulation of xanthine dehydrogenase formation in a strain of Streptomyces cyanogenus was studied in the presence and absence of various carbon and nitrogen sources. If glucose and ammonium were added together to medium, almost no increase was observed in the enzyme activity. The enzyme formation appeared to be influenced at the level of transcription. If glucose but no ammonium was added, the increase in the activity was also reduced although moderately, and the effect seemed to be at the level of translation. Glucose was not only inhibitory to the enzyme formation but also transitorily promotive upon the addition to medium. If glucose or glucose and ammonium were removed from medium, the formation of xanthine dehydrogenase was relieved of the repression and induced by hypoxanthine, xanthine and 6, 8-dihydroxypurine. Intracellular free amino acids were found to decrease considerably under the conditions where the enzyme could be synthesized. Hypoxanthine appeared to be utilized as nitrogen source by the organism, and, therefore, the role of the regulation of xanthine dehydrogenase formation has been discussed in terms of nitrogen metabolism of this organism.
