Binding of sodium aurothiomalate to human serum albumin in vitro at physiological conditions.

The binding of aurothiomalate to human serum albumin was studied by equilibrium dialysis at 37 degrees C, pH 7.3-7.4, and ionic strength 0.15-0.16 mol/l. It was found that aurothiomalate was bound to albumin at one site with an apparent association constant K1 = 3.0 X 10(4) M-1 and at three or more sites with the sum of association constants of the order of 10(3) M-1. Valuable information of the aurothiomalate-albumin interaction was deduced from the observed changes of pH of the albumin solutions during dialysis. A conceivable binding mechanism consistent with the results might be that aurothiomalate binds as Au+ to the high affinity binding site by exchanging a H+ and that this site might be the sulphydryl group in cysteine34; and that aurothiomalate binds as monomeric anions to the lower affinity binding sites.