Isolation and purification of multiple forms of gamma-glutamyl transpeptidase from rat brain

Four different forms of the enzyme gamma-glutamyl transpeptidase were isolated from rat brain by chromatography on concanavalin A. An approximate 1500-fold purification was achieved. The four forms were characterized with respect to molecular weight, Km for gamma-glutamyl-p-nitroanilide, mobility on polyacrylamide gels, and inhibitory effects of borate-serine. The multiple forms of the enzyme were found to have molecular weights ranging from 74,000 to 234,000 and Kms of 0.07 to 8.6 mM. It was determined that in brain, the major portion of the enzyme activity is associated with plasma membrane fragments and endoplasmic reticulum.