ISOLATION AND PROPERTIES OF GAMMA-L-GLUTAMYLCYCLOTRANSFERASE FROM HUMAN BRAIN

Y-L-Giutamylcyclotransferase, which catalyzes the conversion of certain γ-L-glutamyl-L-amino acids into pyrrolidonecarboxylic acid and amino acid, has been purified more than 1000-fold from human and sheep brain.A convenient assay has been devised in which γ-L-glutamyl-γ-L-glutamyl-p-nitroanilide is used as the substrate. The enzyme converts this substrate into pyrrolidonecarboxylic acid and γ-L-glutamyl-pnitroanilide; the latter compound is much more labile to alkali than the substrate and therefore, after standardized alkaline hydrolysis, the product may be quantitatively determined. The enzymatic reaction has also been followed by a new assay for pyrrolidonecarboxylic acid based on its high absorbance at 205 mμ. The purified enzyme acts on the γ-L-glutamyl derivatives of L-glutamine, L-alanine, L-α-aminobutyric acid, and glycine, but is inactive toward glutathione, γ-glutamyl-p-nitroanilide, and certain other γ-glutamylamino acids. Studies carried out with mixtures of 7-glutamylcyclotransferase and γ-glutamyltranspeptidase suggest that the previously observed conversion of glutathione into pyrrolidonecarboxylate involves the intermediate formation of 7-glutamylglutathione. Several possible metabolic functions of the enzyme are considered. © 1969, American Chemical Society. All rights reserved.