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 bound glycoenzyme, the saccharide moiety of which is rather heterogeneous and organ specific. It has been stated that GGT catalyses three types of reactions, i.e., hydrolysis, transpeptidation and autotranspeptidation. The initial velocity equation, involving all these reactions, is shown in the present report. Mathematical analysis of the equation resulting in a definition of the constant of half saturation (Khs). The value of Khs was used for characterization of kinetics of GGT from rat organs differing in the structure of GGT oligosaccharide chains. No significant organ differences were found, when the Khs values of GGT from the brain, kidney and pancreas equalled 0.61 mM, 0.68 mM and 0.68, respectively. On the contrary, when two different glycoforms of GGT from the pancreas were compared, distinct values of Khs were obtained (1.43 mM and 0.67 mM, respectively). It is therefore being suggested that the saccharide chains of GGT are involved in its kinetic properties. However, this effect is masked when the enzyme, non-fractionated into glycoforms, is analysed, even though the saccharide moiety is specific for the organ studied.
Institute of Physiology, Academy of Sciences of the Czech Republic, Prague, Czech Republic.
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Dvoráková
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Krůsek
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Stastný
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Lisý
D000818:Animals; D001921:Brain / Q000201:enzymology; D002846:Chromatography, Affinity; D003208:Concanavalin A / Q000378:metabolism; D005260:Female; D006023:Glycoproteins / Q000378:metabolism; D007668:Kidney / Q000201:enzymology; D007700:Kinetics; D009844:Oligosaccharides / Q000737:chemistry; D010179:Pancreas / Q000201:enzymology; D051381:Rats; D017208:Rats, Wistar; D013154:Spleen / Q000201:enzymology; D005723:gamma-Glutamyltransferase / Q000737:chemistry / Q000378:metabolism*
D006023:Glycoproteins; D009844:Oligosaccharides; D003208:Concanavalin A; D005723:gamma-Glutamyltransferase