Studies on the properties of the variants of gamma-glutamyl transpeptidase in human urine.

ABSTRACT

Both the high molecular weight and the low molecular weight variants of urinary Y-glutamyl transpeptidase, displayed transpeptidase (pH optimum 8.6) and autotranspeptidase (pH optimum 9.4) activities. Iodoacetamide inhibited the transpeptidase activity more efficiently than the autotranspeptidase activity with respect to both variants of Yglutamyl transpeptidase. The high molecular weight form utilized L-glutamine as a better acceptor than L-cystine during the transpeptidation reaction whereas the reverse was the case with the low molecular weight variant. While phenylmethylsulphonyl fluoride-treated enzymes retained full activities per se, addition of maleic acid to the modified enzyme was found to inhibit the catalytic activities indicating a maleic acid-induced conformational change of the modified enzyme.