Purification and Properties of γ-Glutamyl Cyclotransferase from Pig Liver

Abstract

The widely occurring enzyme γ-glutamyl cyclotransferase acts on γ-glutamyl peptides to effect the release of the terminal glutamyl residue as the cyclic derivative pyrrolidone carboxylic acid. The enzyme has been purified from pig liver by (1) ammonium sulfate precipitation from the supernatants of homogenates, (2) CM-cellulose treatment, (3) DEAE-Sephadex chromatography, and (4) preparative polyacrylamide gel electrophoresis. The homogeneity of the highly purified enzyme was demonstrated by ultracentrifugation and electrophoretic analyses. By means of (5) isoelectric focusing, two forms of the enzyme with isoelectric points 4.87 and 4.95 were separated. These forms proved to have very similar sedimentation velocities, molecular weights, and amino acid compositions, and to have the same amino acid, glycine, as the N-terminal residue.