SUMMARY: NCTC 8203 was shown to metabolize guanine by deamination to xanthine, which was then oxidized to uric acid and further products. Guanine deaminase activity was present in non-induced bacteria but was 3-4 times greater in guanine-induced bacteria. Xanthine oxidase, and the uric acid oxidizing enzymes, were not found in bacteria grown in a minimal salts medium but were induced by adding guanine or xanthine to the culture medium towards the end of the growth period. When uric acid was added, only the uric acid oxidizing enzymes were induced. Enzyme induction also occurred when washed suspensions of the bacteria were incubated with guanine, xanthine or uric acid in Warburg flasks. 8-Azaguanine was deaminated more rapidly than guanine by non-induced bacteria and the rate was again greater with guanine-induced bacteria. 8-Azaguanine and 8-azaxanthine were not oxidized and did not induce the synthesis of deaminases or oxidases. 8-Azaguanine and 8-azaxanthine had no effect on the oxidation of guanine, xanthine or uric acid by fully induced bacteria. Equimolar concentrations of 8-azaguanine inhibited adaptation to the oxidation of guanine, xanthine and uric acid when added before the substrates. 8-Azaxanthine, under the same conditions, delayed adaptation to guanine and xanthine oxidation, and completely inhibited adaptation to uric acid. Mutant strains were isolated which were resistant to 10 mM-8-azaguanine and 5 mM-8-azaxanthine which completely inhibited growth of the parent strain. Another class of mutants was isolated resistant to 8-azaguanine and not resistant to 8-azaxanthine. Both classes of mutants were indistinguishable from the parent strain in their susceptibility to 8-azaguanine and 8-azaxanthine inhibition of adaptation to purine oxidation.


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