An electrophoretic investigation of interactions between bovine plasma albumin and charged dextran derivatives

Abstract

An electrophoretic in-vestigation of the formation of soluble interaction complexes between bovine plasma albumin and charged dextran derivatives (sulphate esters and diethylaminoethyl ethers) is described. The investigation is limited to conditions of pH such that the net charge on the protein and the charge on the polyelectrolyte have the same signs. In the dextran sulphate systems soluble complex formation is maximal at the isoelectric pH of the protein and decreases with increasing pH. Complexes cannot be detected above pH 8.5. Complex formation decreases with increasing ionic strength. The equilibrium constant for complex formation is calculated from the electrophoresis results under one set of conditions which constitute a special case of the theory of Gilbert and Jenkins. Dextran amine is shown to suppress the albumin isomerization reaction at pH 4.0. Except for this observation, no evidence has been obtained for complex formation between the bovine plasma albumin and the dextran amines. The mobility of bovine plasma albumin at I 0.10, 0 , is determined as a function of pH. Deviations from simple electrophoretic behavior expected in the absence of interaction in the systems studied are evaluated with the moving-boundary theory for strong electrolytes.