Regulation der Biosynthese der aromatischen Aminosäuren in Saccharomyces cerevisiae

We have studied the repression of the first enzymes of the main branch and the pathways after the branchpoint in the aromatic biosynthesis of Saccharomyces cerevisiae . Anthranilate synthetase is repressed by l ‐tryptophan and prephenate dehydratase by l ‐phenylalanine. 3‐Deoxy‐ d ‐arabinoheptulosonic acid 7‐phosphate (DAHP) synthetases are not repressed by l ‐phenylalanine, l ‐tyrosine and l ‐tryptophan, chorismate mutases are repressed neither by l ‐phenylalanine nor by l ‐tyrosine, and prephenate dehydrogenase shows no repression by l ‐tyrosine. l ‐Tryptophan exhibits an induction of the chorismate mutase. Besides chorismate mutase is activated by l ‐tryptophan. l ‐Phenylalanine exhibits an induction and also an activation of the prephenate dehydrogenase. By simultaneous addition of l ‐tryptophan, l ‐phenylalanine, and l ‐tyrosine p ‐aminobenzoic acid was accumulated and the production of p ‐aminobenzoate synthetase was induced. The tyrosine‐sensitive and phenylalanine‐sensitive isoenzymes of DAHP synthetase belong to the V‐system of the allosteric enzymes. Chorismate mutase and prephenate dehydrogenase are members of the K‐system. In an earlier publication we have discussed the feedback inhibition of the described enzymes. In this paper we discuss the whole events of the regulation phenomena in Saccharomyces cere‐visiae . We also considered the degradation of l ‐tryptophan, l ‐phenylalanine, and l ‐tyrosine to tryptophol, phenylethanol, and tyrosol respectively in connection with the regulatory events.