Anthranilate phosphoribosyltransferase (PRT), the second-step enzyme in the tryptophan specific biosynthetic pathway of Brevibacterium flavum, was inhibited by l-tryptophan but not by d-tryptophan, l-phenylalanine or l-tyrosine at all. The pattern of the inhibition by various tryptophan analogs was quite different from that of anthranilate synthase (AS), the first-step enzyme in the pathway. The concentration of trytophan giving 50% inhibition of PRT and the inhibitor constant for tryptophan, Ki, were 0.15 and 0.26 mM, respectively. The inhibition of PRT was noncompetitive for both the substrates, anthranilate and phosphoribosylpyrophosphate. Gycerol increased the sensitivity to the tryptophan inhibition as well as the activity, whereas KCl and NaCl stimulated the PRT activity alone. In all the mutants tested, the feedback inhibition of PRT was removed concomitantly with that of AS. When phenylalanine tyrosine double auxotrophs having derepressed levels of the tryptophan enzymes were cultured under tyrosine-limitation, they accumulated anthranilate but not tryptophan, as did those having normal repression control. These results were concluded to be due to the presence of the feedback inhibition by tryptophan of PRT. In Bacillus subtilis K, the inhibition by tryptophan of PRT was much weaker than that in B. flavum and almost the same as that in B. flavum mutants having PRT resistant to the feedback inhibition. PRT in a tryptophan-producing mutant of B. subtilis was similar to the wild-type enzyme.
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Sugimoto et al. (1983) studied this question.