Aromatic biosynthesis in yeast: I. The synthesis of tryptophan and the regulation of this pathway

Abstract

1. 1. The enzymatic functions of the tryptophan path of Saccharomyces cerevisiae have been found to be the same as reported for Aerobacter aerogenes and Escherichia coli. 2. 2. It was concluded that the locus tr-3 codes for a polypeptide necessary for two enzymic functions, anthranilate synthetase and indoleglycerol phosphate synthetase. Evidence is presented showing that the gene tr-4 codes for anthranilate phosphoribosylpyrophosphate phosphoribosyltransferase and tr-1 for phosphoribosylanthranilic acid isomerase. It was deduced that tr-2 codes for a plypeptide necessary for anthranilate synthetase. 3. 3. The stability of the anthranilate synthetase of Saccharomyces cerevisiae was markedly dependent on pH with an optimum stability in Tris buffer at pH 7.25. The enzyme from Aerobacter aerogenes was relatively pH stable. This finding is used to support the view that in Saccharomyces cerevisiae anthranilate synthetase and indoleglycerol phosphate synthetase form an aggregate enzyme molecule. 4. 4. In yeast, anthranilate synthetase is controlled by end-product inhibition and repression. The control of anthranilic acid synthesis by exogenous tryptophan is less efficient for Saccharomyces cerevisiae than for Escherichia coli.