SUMMARY: The characteristics of an induced enzyme system responsible for the degradation of -histidine by a soil organism were studied. Induction could be achieved by exposing cells to -histidine, -histidine, urocanate, β-alanyl--histidine or -histidyl--histidine, but not by exposure to a variety of other imidazoles. The kinetics of induction by - and -histidine differed considerably and the -isomer was shown to be metabolized only very slowly by fully induced cells. Chloramphenicol and --fluorophenylalanine strongly inhibited enzyme synthesis, whilst a variety of purine and pyrimidine analogues were without effect. Nitrogen starvation of non-induced cells decreased but did not completely prevent the appearance of the enzyme system on induction with -histidine. Non-induced cells possess a low level of ‘basal’ enzymes before exposure to an inducing substance.


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