Regulation of the biosynthetic pathway of aromatic amino acids in Nocardia mediterranei.

The regulation of enzymes in the biosynthetic pathway of aromatic amino acids in Norcardia mediterranei was studied. Anthranilate synthase was sensitive to feedback inhibition by very low concentrations of LTrp, and kinetic analysis showed that LTrp was competitive with respect to chorismate; the five enzymes in LTrp biosynthesis pathway, anthranilate synthase (AS), anthranilate-phosphoribosylpyrophosphate phosphoribosyltransferase (PRT), N-5'-phosphoribosylanthranilate isomerase (PRAI), indole-3-glycerol phosphate synthetase (InGPS) and tryptophan synthase (TS), were all repressed by LTrp; LTyr and LPhe inhibited chorismate mutase. Prephenate dehydratase activity was greatly inhibited by LPhe and activated by LTyr, nearly 60% of its activity was inhibited by 5 microM of LPhe, and 20 microM of LTyr increased the activity approx. 3-fold. In addition, the effects of LPhe and LTyr on prephenate dehydratase were highly specific. The regulatory circuit of the biosynthetic pathway of aromatic amino acids in N. mediterranei is presented.