In vivo and in vitro studies on the binding of salicylate to human plasma proteins: evidence for one type of binding site.

In vivo and in vitro binding of salicylate to plasma proteins was studied by ultrafiltration at room temperature. The nonlinearity of the Scatchard and Klotz plots were explained by the presence of lipid-soluble substances in plasma. Delipidation of plasma resulted in changes of the binding characteristics of plasma in that more moles of salicylate could be bound per mole of protein. This changed the appearances of the Scatchard and Klotz plots so that a much larger range of salicylate concentration could be accommodated by the linear portion of the graphs. The equilibrium constant for the in vitro salicylate binding was identical for the delipidated and untreated plasma. However, the in vivo binding constant for salicylate in plasma was higher than the in vitro binding constant.