The binding of aurothiomalate to plasma proteins in vitro.

The physicochemical factors responsible for the aurothiomalate-albumin interaction were studied by a thermodynamic analysis of the binding of the anion to bovine albumin. The binding process was entropically driven and it was concluded that electrostatic bonding formed the basis of the aurothiomalate-albumin interaction. The binding of aurothiomalate to human plasma proteins at 37 degrees C and pH 7.45 and the modification of its binding by indomethacin and phenylbutazone was studied by ultrafiltration. Aurothiomalate was bound to human plasma albumin at a single site with an affinity constant of 6.1 X 10(3) M-1 and also at several sites of lower affinity. The plasma protein binding of the anion was increased in the presence of indomethacin and phenylbutazone. At therapeutic concentrations in vitro phenylbutazone significantly increased the plasma protein binding of aurothiomalate.