The effect of pH on the transpeptidation and hydrolytic reactions of rat kidney gamma-glutamyltransferase

Biochim Biophys Acta. 1985 Nov 29;832(2):142-7. doi: 10.1016/0167-4838(85)90325-5.


The effect of pH upon the transpeptidation and hydrolytic reactions of gamma-glutamyltransferase [5-glutamyl)-peptide:amino-acid 5-glutamyltransferase, EC have been investigated. It was found that the enzyme was irreversibly inactivated below pH 7.5 or above pH 9.4. Transpeptidation was markedly pH-dependent, while hydrolysis was pH-independent. The pH optimum for transpeptidation was found to vary for different acceptors. The ascending limb of the pH-optimum curve is attributed to the pK of the alpha-amino group of the acceptor, while the descending limb of the pH-optimum curve is attributed to an ionisable group in the active site of the enzyme. These observations provide much information about the interaction of the enzyme with the acceptor: (1) the true acceptor for gamma-glutamyltransferase is the deprotonated form of the amino acid; (2) glycylglycine has a similar acceptor activity to methionine, its apparent higher activity being due to the low pK of the alpha-amino group; (3) the enzyme is reversibly inactivated at higher pH by the deprotonation of a group in the active site which is involved in both binding of acceptor and catalysis of transpeptidation (this group is not involved in the hydrolysis reaction); (4) at pH 8.5, the normal pH for assay, only 47% of the enzyme is active, while at pH 7.4 gamma-glutamyltransferase is 93% in the active form.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Chemical Phenomena
  • Chemistry
  • Hydrogen-Ion Concentration
  • Hydrolysis
  • Kidney / enzymology*
  • Kinetics
  • Rats
  • gamma-Glutamyltransferase*


  • gamma-Glutamyltransferase