52] γ-Glutamylcyclotransferase from rat kidney

Abstract

γ-Glutamylcyclotransferase catalyzes the conversion of γ-glutamyl amino acids to 5-oxoproline and the corresponding free amino acid. The enzyme is widely distributed in mammalian tissues and is highly active toward the L-γ-glutamyl derivatives of glutamine, methionine, alanine, cysteine, cystine, and several other amino acids. The most highly purified preparations of the enzyme are obtained from rat kidney. In one procedure for isolation of the enzyme, chromatography on thiol-Sepharose is used. In another procedure, the crude enzyme is treated with dithiothreitol and then with iodoacetamide. These procedures are described in this chapter. The properties of the purified enzyme preparations are also reviewed. Molecular weight determinations carried out by sodium dodecyl sulfate-polyacrylamide gel electrophoresis with appropriate standards give a value of 27,000 for the molecular weights of both the pI 4.6 and pI 5.1 forms of the enzyme. Both forms of the enzyme exhibit identical ultraviolet absorption characteristics with a maximum at 279 nm.