par Penninckx, Michel 
;Jaspers, Charles
Référence Biochimie, 67, 9, page (999-1006)
Publication Publié, 1985
;Jaspers, Charles Référence Biochimie, 67, 9, page (999-1006)
Publication Publié, 1985
Article révisé par les pairs
| Résumé : | In a foregoing paper we have shown the presence in the yeast Saccharomyces cerevisiae of an enzyme catalyzing the hydrolysis of L-γ-glutamyl-p-nitroanilide, but apparently distinct from γ-glutamyltranspeptidase. The cellular level of this enzyme was not regulated by the nature of the nitrogen source supplied to the yeast cell. Purification was attempted, using ion exchange chromatography on DEAE Sephadex A 50, salt precipitations and successive chromatographies on DEAE Sephadex 6B and Sephadex G 100. The apparent molecular weight of the purified enzyme was 14,800 as determined by gel filtration. As shown by kinetic studies and thin layer chromatography, the enzyme preparation exhibited only hydrolytic activity against γ-glutamylarylamide and L-glutamine with an optimal pH of about seven. Various γ-glutamylaminoacids, amides, dipeptides and glutathione were inactive as substrates and no transferase activity was detected. The yeast γ-glutamylarylamidase was activated by SH protective agents, dithiothreitol and reduced glutathione. Oxidized glutathione, ophtalmic acid and various γ-glutamylaminoacids inhibited competitively the enzyme. The activity was also inhibited by L-γ-glutamyl-o-)carboxy)phenylhydrazide and the couple serine-borate, both transition-state analogs of γ-glutamyltranspeptidase. Diazooxonorleucine, reactive analog of glutamine, inactivated the enzyme. The physiological role of yeast γ-glutamylarylamidase-glutaminase is still undefined but is most probably unrelated to the bulk assimilation of glutamine by yeast cells. © 1985 Masson, Paris. |
