Nucleoside-catabolizing enzymes in Salmonella typhimurium. Introduction by ribonucleosides.

Abstract

Addition of cytidine, uridine or adenosine to glycerol‐grown cultures of Salmonella typhimurium induces the synthesis of cytidine deaminase and uridine phosphorylase (the cyt‐enzymes) as well as the synthesis of thymidine phosphorylase, deoxyriboaldolase, phosphodeoxyribomutase and purine nucleoside phosphorylase (the deo‐enzymes).The inducing effect of adenosine is more pronounced in mutant strains deficient in adenosine catabolism.A regulatory mutant which synthesizes the cyt‐enzymes constitutively has been isolated. This mutant also synthesizes the deo‐enzymes in elevated amounts. However, the level of the deo‐enzymes in the regulatory mutant like in wild‐type cells can be raised further if thymidine is added to the medium.The synthesis of the cyt‐enzymes appears to be sensitive to catabolite repression.From induction experiments carried out in mutant strains restricted in their metabolism of cytidine and uridine it appears that both compounds may act as inducer.Strains unable to metabolize cytidine or uridine contained increased levels of the cyt‐ and the deo‐enzymes even in the absence of external inducer. This is most likely due to endogenous induction by cytidine or uridine.