Enhanced Co2+ activation and inhibitor binding of carboxypeptidase M at low pH. Similarity to carboxypeptidase H (enkephalin convertase)

Biochem J. 1989 Jul 1;261(1):289-91. doi: 10.1042/bj2610289.


Carboxypeptidases H and M differ in their distribution and other properties, but both are activated by Co2+ and inhibited by guanidinoethylmercaptosuccinic acid. The higher degree of activation or inhibition of carboxypeptidase H by these agents at acid pH has been employed to identify this enzyme in tissues. We found that the activation or inhibition of both purified and plasma-membrane-bound human carboxy-peptidase M depends on the pH of the medium. CoCl2 activated over 6-fold at pH 5.5, but less than 2-fold at pH 7.5. Guanidinoethylmercaptosuccinic acid inhibited the membrane-bound carboxypeptidase M more effectively than the purified enzyme, and the IC50 was about 25-30 times lower at pH 5.5. As purified human plasma carboxypeptidase N and pancreatic carboxypeptidase B were also activated more at pH 5.5, we conclude that the increased activation by CoCl2 is due to the enhanced dissociation of Zn2+ below the pKa of the ligands that co-ordinate the cofactor in the protein. Thus increased activation or inhibition at acid pH would not differentiate basic carboxypeptidases.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Cobalt / pharmacology*
  • Enzyme Activation
  • GPI-Linked Proteins
  • Humans
  • Hydrogen-Ion Concentration
  • Metalloendopeptidases / antagonists & inhibitors
  • Metalloendopeptidases / metabolism*
  • Microvilli / enzymology
  • Succinates / pharmacology*


  • GPI-Linked Proteins
  • Succinates
  • Cobalt
  • guanidinoethylmercaptosuccinic acid
  • carboxypeptidase M
  • Metalloendopeptidases
  • cobaltous chloride