Variants of 7-glutamyl transferase in human urine

Abstract

When dialyzed human urine was subjected to ultracentrifugation, gamma glutamyl transferase activity amounting to one-third or less of the total activity was found associated with the microsomal fraction and the remaining in the 100 000 X g supernatant. By ion-exchange chromatography on DEAE-cellulose at pH 7.5, the urinary enzyme was resolved into two fractions. The less anionic form (eluted with 0.15 mol/l NaCl) corresponded to the 100 000 X g supernatant fraction. The more anionic form (eluted with 0.5 mol/l NaCl) corresponded to the microsomal fraction. On chromatography on concanavalin A-sepharose, the urinary transferase activity separated into the unbound fraction and the bound fraction (eluted with α-methyl- d-glucoside). The bound fraction was retained more tightly on DEAE-cellulose (eluted with 0.5 mol/l NaCl). The unbound fraction had weaker interaction with the ionic-exchanger (eluted with 0.15 mol/l NaCl). Each of two fractions separated by affinity chromatography on concanavalin A-sepharose, resolved into two bands on cellulose acetate electrophoresis at pH 7.5. In addition, during gel chromatography on Sephadex G-200, they separated into a high molecular weight (>200000) fraction and a low molecular weight (55000) fraction. The band that stayed at the origin during electrophoresis was high molecular weight in nature, whereas the fraction that moved towards the anode was found to be the smaller form of the enzyme. The study of the variants of urinary gamma glutamyl transferase was not found to be of clinical significance. The nature and origin of the variant forms of the enzyme in urine are discussed.