Summary: Both co-ordinate and sequential inductions govern the synthesis of the enzymes required for the oxidative dissimilation of l-tryptophan by a strain of The first two enzymes of the sequence, tryptophan pyrrolase and formylkynurenine formamidase, are induced co-ordinately by l-kynurenine, the product of their successive action on l-tryptophan; l-trytophan itself is not an inducer. Both these enzymes are present at low concentrations in uninduced organisms, so that inducer is generated endogenously when such organisms are exposed to an exogenous supply of l-tryptophan. l-Kynurenine also induces formation of the third enzyme of the sequence, kynureninase, which is not detectable in uninduced bacteria. Although it is elicited by the same inducer, synthesis of kynureninase is not co-ordinate with the syntheses of pyrrolase and formamidase; the induction of kynureninase can accordingly be considered as the first sequential inductive step in the pathway. It is immediately followed by another sequential inductive step: the synthesis of anthranilic acid oxidase, elicited by anthranilic acid, which is formed from kynurenine through the action of kynureninase.


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