The dye uptake of native and modified serum proteins

The interaction of normal and specifically modified human serum albumins with the sulphonphthalein dyes has been studied in solution. Special attention has been directed to the interaction with bromocresol green. With normal unmodified albumin, the total dye uptake does not alter significantly between pH 2.0 and 5.0, but the dye bound in the quinoid form increases with rise in pH. With the deaminated albumin, the dye binding fell with rise in pH, while the amount of bound quinoid form remained constant from pH 3.5 upwards. It appears, therefore, that in the binding of bromocresol green by human albumin, two different sites are involved between pH 2.0 and 5.0, and that above pH 3.5, the predominating site of interaction is the free amine groups of the albumin.