Cadmium binding to human alpha 2-macroglobulin

Biochim Biophys Acta. 1984 Dec 21;791(3):370-4. doi: 10.1016/0167-4838(84)90349-2.


alpha 2-Macroglobulin (alpha 2M) is one of the major cadmium-binding proteins of human plasma. As determined with equilibrium dialysis, alpha 2M bound 4.6 (+/- 0.7) mol Cd2+ per mol protein with an apparent dissociation constant of (9.6 (+/- 5.0] X 10(-7) M. Methylamine-modified alpha 2M (alpha 2M-Me) had a similar affinity for Cd2+ (Kd,app = 5.3 X 10(-7) M), but fewer binding sites. Cadmium produced a small increase in the amidolytic activity of trypsin in the presence of alpha 2M and soybean trypsin inhibitor. Using the binding parameters determined from the equilibrium dialysis studies, the Cd2+ concentration which produced a half-maximal increase in amidolytic activity corresponded to saturation of all Cd2+-binding sites in one-half of the alpha 2M molecules. From these results, a model is proposed in which one Cd2+-binding site is present in each of the four polypeptide chains which compose alpha 2M.

Publication types

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

MeSH terms

  • Cadmium / blood*
  • Cadmium / pharmacology
  • Cadmium Chloride
  • Electrophoresis, Polyacrylamide Gel
  • Humans
  • Immunodiffusion
  • Kinetics
  • Protein Binding
  • Trypsin / metabolism
  • alpha-Macroglobulins / metabolism*


  • alpha-Macroglobulins
  • Cadmium
  • Trypsin
  • Cadmium Chloride