The donor specificity and kinetics of the hydrolysis reaction of gamma-glutamyltransferase.
The donor specificity of the hydrolytic reaction of gamma-glutamyltransferase [5-glutamyl)-peptide:amino-acid 5-glutamyltransferase, EC 2.3.2.2) has been studied by the use of specifically synthesised gamma-glutamyl substrates. It was found that a wide variety of gamma-glutamylated adducts were hydrolysed by the enzyme. The structure of the adduct was relatively unimportant for donor specificity and the enzyme appears to 'recognise' the gamma-glutamyl portion of the donor molecule. In particular the alpha-amino group and the free proton of the gamma-peptide bond appear to be essential for donor activity. The Vmax of hydrolysis increased proportionally to the electron-withdrawing capacity of the adduct moiety. The rate of formation of gamma-glutamyl-enzyme intermediate was therefore dependent upon the structure of the adduct of the gamma-glutamyl donor. The results suggest that the enzyme shows little specificity beyond that for gamma-glutamyl amides and there is therefore no reason to postulate the presence of a specific glutathione-binding site.
D000818:Animals; D001665:Binding Sites; D006868:Hydrolysis; D007668:Kidney / Q000201:enzymology; D007700:Kinetics; D011487:Protein Conformation; D051381:Rats; D013379:Substrate Specificity; D005723:gamma-Glutamyltransferase / Q000378:metabolism*
D005723:gamma-Glutamyltransferase