A kinetic study on the distribution of Cu(II)-ions between albumin and transferrin

Serum albumin ( human, bovine) has a specific Cu(II)-ion binding site, and is proposed to act as a copper transport protein in blood plasma. Human transferrin, normally about 30% saturated with iron in vivo, has two sites/molecule capable of complexing Cu( II); one more strongly than the other ( Hirose et al. 1996). The present study shows that this binding site has a slightly stronger affinity for Cu( II) than that on the albumins. However, both human- and bovine albumin could take up part of the transferrin bound Cu( II), the second order rate constant for the reaction estimated to 12 mM(-1) min(-1) for both species. In vivo the albumin concentration is considerably higher than that of iron-free transferrin, and it seems unlikely that the latter can compete with albumin for non-ceruloplasmin cupric ions.