Multiple regulation of nucleoside catabolizing enzymes in Escherichia coli: Effects of 3:5′ cyclic AMP and CRP protein
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The regulation of the synthesis of nucleoside metabolizing enzymes has been studied in cya and crp mutant strains of Escherichia coli.
The synthesis of the cyt-enzymes, cytidine deaminase and uridine phosphorylase regulated by the cytR gene product, is activated by the cAMP-CRP complex. On the other hand the synthesis of the deoenzymes: deoxyriboaldolase, thymidine phosphorylase, phosphodeoxyribomutase and purine nucleoside phosphorylase, appears to be increased if an active cAMP-CRP complex cannot be formed.
It also seems that nucleosides serve as poor carbon sources for cya and crp mutants; this could not solely be explained by low levels of nucleoside metabolizing enzymes nor by a deficiency in nucleoside uptake. Addition of casamino acids stimulated the growth of cya and crp mutants, with nucleosides as carbon sources. When grown on glucose and casamino acids growth could be stimulated by adenine and hypoxanthine nucleosides; these results suggest an impaired nitrogen metabolism in cya and crp mutants.
EnzymesPurine nucleoside phosphorylase or purine nucleoside: orthophosphate (deoxy) ribosyltransferase (EC 184.108.40.206) thymidine phosphorylase or thymidine: orthophosphate deoxyribosyltransferase (EC 220.127.116.11) uridine phosphorylase or uridine: orthophosphate ribosyltransferase (EC 18.104.22.168) cytidine deaminase or (deoxy) cytidine aminohydrolase (EC 22.214.171.124) deoxyriboaldolase or 2-deoxy-D-ribose-5-phosphate acetaldehydelase (EC 126.96.36.199) phosphodeoxyribomutase (EC 188.8.131.52)
Abbreviations and Symbols
cyclic adenosine 3:5′-monophosphate
cAMP receptor protein. Genes coding for: adenyl cyclase
cAMP receptor protein
purine nucleoside phosphorylase
- pup; cytR
regulatory gene for cdd, udp, dra, tpp, drm, and pup
regulatory gene for dra, tpp, drm, and pup
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