RELATIONSHIP BETWEEN KINETIC-PROPERTIES OF GAMMA-GLUTAMYL-TRANSPEPTIDASE AND THE STRUCTURE OF ITS SACCHARIDE MOIETY

Gamma-glutamyl transpeptidase (EC 2.3.2.2; GGT) is a plasma-membrane b ound glycoenzyme, the saccharide moiety of which is rather heterogeneo us and organ specific. It has been stated that GGT catalyses three typ es of reactions, i.e., hydrolysis, transpeptidation and autotranspepti dation. The initial velocity equation, involving all these reactions, is shown in the present report. Mathematical analysis of the equation resulted in a definition of the constant of half saturation (K-hs). Th e value of K-hs was used for characterization of kinetics of GGT from rat organs differing in the structure of GGT oligosaccharide chains. N o significant organ differences were found, when the K-hs values of GG T from the brain, kidney and pancreas equalled 0.61 mM, 0.68 mM and 0. 68 mM, respectively. On the contrary, when two different glycoforms of GGT from the pancreas were compared, distinct values of K-hs were obt ained (1.43 mM and 0.67 mM, respectively). It is therefore being sugge sted that the saccharide chains of GGT are involved in its kinetic pro perties. However, this effect is masked when the enzyme, non-fractiona ted into glycoforms, is analysed, even though the saccharide moiety is specific for the organ studied.