SUMMARY: Three enzymes catalysing the synthesis of four intermediates (phosphoribosylglycinamide, phosphoribosylaminoimidazole-succinocarboxamide, phosphoribosylaminoimidazole-carbox-amide and AMP) in the purine biosynthetic pathway were detected in extracts of and , even when the organisms had been grown in mice. However only one of the three enzymes, adenylosuccinate AMP-lyase (catalysing the synthesis of the last two of the four intermediates listed above) was detected in . Phosphoribosyltransferases, which convert adenine, guanine and hypoxanthine to the corresponding nucleoside monophosphates, and adenosine kinase were the major enzymes for purine scavenging in all mycobacteria studied. In contrast to enzymes in the synthetic pathway, evidence for metabolic regulation of the purine-scavenging enzymes was obtained. In particular, 20-80-fold differences in the activities of guanine phosphoribosyltransferase and adenosine kinase were observed when was grown in media with or without purines, or in mice. In , activities of all phosphoribosyltransferases were low in comparison with activities in and (specific acitivity <2% when comparisons were made between extracts of host-grown mycobacteria). However, activity of adenosine kinase was higher in host-grown than in host-grown or .


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