title: gamma-Glutamyltransferase is not involved in the bulk uptake of amino acids, peptides or gamma-glutamyl-amino acids in yeast (Saccharomyces cerevisiae).
abstract: gamma-Glutamyltransferase activity has been measured in yeast (Saccharomyces cerevisiae) and shown to be associated mainly with the membrane fraction. A similar level of activity is found in a wild-type strain and in gap and gpp strains, the latter mutants being defective in the general amino acid and peptide permeases respectively. The activity is inhibited in whole cells by 6-diazo-5-oxo-L-norleucine (N2O-Nle), azaserine and serine-borate complex; this inactivation seemingly acts from without, for it is similar in (i) control and dicyclohexylcarbodi-imide-treated cells and in (ii) the wild-type and a gap mutant, a treatment and a mutation that it has been shown prevents uptake of the inhibitors. Thus a major portion of the gamma-glutamyltransferase activity appears to exist in a membrane-bound form that is orientated with its gamma-glutamyl-binding site facing the outside. Yeast cells in which gamma-glutamyltransferase has been inactivated by N2O-Nle show no significant change in their rates of uptake of a variety of amino acids, dipeptides and gamma-glutamyl-amino acids. The results preclude a major, direct role for gamma-glutamyltransferase in the transport of these substrates.
mesh_terms: D000596:Amino Acids / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D003980:Diazooxonorleucine / Q000494:pharmacology; D009154:Mutation; D010455:Peptides / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000201:enzymology*; D005723:gamma-Glutamyltransferase / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D000596:Amino Acids; D010455:Peptides; D003980:Diazooxonorleucine; D005723:gamma-Glutamyltransferase