Calculations of the distribution of zinc in a computer model of human serum

During the last decade, investigators employing a wide variety of separation techniques have reported that serum albumin, rather than serum transferrin, is the major carrier protein for labile zinc. However, in contrast to these studies, a simple comparison of the zinc binding constants for albumin and transferrin suggests a significant role for transferrin with regard to serum zinc transport. In the present study multicomponent equilibrium calculations that incorporate recently determined binding constants for zinc-transferrin as well as equilibrium constants for the binding of bicarbonate, sulfate and phosphate to apotransferrin have been used to model the distribution of labile zinc in normal human serum. Anion binding has a major impact on the predicted zinc distribution, lowering the percentage of zinc bound to transferrin from 56% to 11%. The model gives approximately 1% zinc as low-molecular-weight complexes. The improved model results are in good agreement with biological studies on the distribution of zinc among serum proteins.