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This paper reports the isolation of a proteinase and a proteinase inhibitor from Saccharomyces cerevisiae S288C (α). The purified proteinase catalyzes the hydrolysis of casein at neutral pH. It inactivates the holo-tryptophan synthase from Neurospora crassa but does not inactivate the holo-ornithine aminotransferase from pig kidney. This proteinase can be inhibited either by phenylmethanesulfonyl fluoride (a specific inhibitor for serine proteases), the sulfhydryl reagent, p-mercuribenzoate, or the endogenous proteinase inhibitor present in yeast. The yeast proteinase inhibitor is a heat-stable material with a molecular weight of approximately 13000. This proteinase inhibitor can protect both yeast and Neurospora tryptophan synthase against proteolytic inactivation. The proteinase and its inhibitor coexist in the yeast extracts. The cellular level of the proteinase and the inhibitor activities varies with the composition of the medium in which the cells are grown. Since some yeast proteinases have been shown to form inactive complexes with their respective inhibitors, it is proposed that proteinase-inhibitor interaction is a possible mechanism for relation of intracellular proteolytic activity. [ABSTRACT FROM AUTHOR]

In the previous paper, a metabolic relationship between a cytochrome oxidase deficiency and threonine biosynthesis in Saccharomyces cerevisiae was proposed. It has been found that high concentrations of threonine or its immediate precursors L-aspartate- β-semi-aldehyde or homoserine, are able to restore cytochrome oxidase synthesis in threonine auxotrophs, grown in the presence of glucose as a carbon source. On the other hand, these strains are able to synthesize cytochrome oxidase when the carbon source is ethanol or glycerol even without an excess of threonine. The results show that this phenomenon is concerned with the regulation of cytochrome oxidase synthesis. Different hypotheses are presented to explain the possible role of threonine in this regulation. One of them stresses the possible role of a differential auxotrophy for the cytoplasmic and the mitochondrial protein synthesis systems. [ABSTRACT FROM AUTHOR]

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 cerevisiae. 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. [ABSTRACT FROM AUTHOR]