Electrophoretic Behavior of Normal Human Serum Albumin at pH 4.0

In the preceding paper on the behavior of pooled normal human serum albumin in various buffers at pH 4.0 (1)) it was demonstrated that the electrophoretic pattern of albumin shows a single moving boundary in the presence of the lower fatty acids, excepting formic and acetic acid, and of certain diand tribasic organic acids. This phenomenon is probably a consequence of the interaction between this protein and the monobasic organic acids mentioned, due to forces between the nonpolar portions of the interactants. The introduction of a hydroxyl or an amino group into the fatty acids with more than two carbon atoms caused significant diminution of the binding and, thus, produced marked changes in the electrophoretic bchavior of the protein. In these media, the electrophoretic patterns showed several moving boundaries. The interaction between albumin and certain other diand tribasic organic acids, such as malonic, ma&c, and citric acid, appeared to be primarily due to electrostatic forces. However, similar organic acids with truns configuration (fumaric acid) did not change the electrophoretic patterns; this points to a steric requirement for this reaction (1). The aim of this paper is to present evidence for the reversibility of the interaction between albumin and organic acids as judged by free electrophoresis at pH 4.0 in r/2 0.1 buffer solutions. Moreover, studies on the effect of biand trivalent metallic ions upon serum albumin, leading to similar observations, are also described.