Glutathione Metabolism in Relation to the Amino‐Acid Permeation Systems of the Yeast Saccharomyces cerevisiae

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Abstract
A careful enzyme specificity analysis has revealed the presence of a typical .gamma.-glutamyltranspeptidase in the yeast S. cerevisiae. The enzyme cellular level is low in the presence of NH4+ as a sole N source and rises when individual amino acids are used as N sources. The .gamma.-glutamyltranspeptidase appears to be repressed by NH4+ and escapes to the regulatory circuits under the control of glutamine and the glutamate-dehydrogenase .cntdot. NH4+ complex. The transpeptidase cellular level is unaffected in mutants which have lost the general amino acid permease and specific systems for L-arginine and L-lysine. In contrast, a low enzyme level is observed when growing an apf mutant on urea; this mutant is most probably affected in a common element shared by all the amino acid permeation systems. Urea appears to be a N source which promotes a high transpeptidase level in the wild-type strain. The reported data are discussed in the light of the current theories about the intervention of glutathione metabolism in the translocation of amino acids.

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