Buffer composition in paper electrophoresis. Considerations on its influence with special reference to the interaction between small ions and proteins

The electrophoretic mobility, both absolute and relative, of different plasma proteins varies with the ionic composition and the ionic strength of the buffer used (1, 2). The linkage between serum albumin and differ-ent anions has been elucidated by Klotz (3), Scatchard et at. (4), and others. Klotz (3) has shown that the association constant between diethyl-barbiturate and albumin is relatively high. Armstrong et at. (5) found the mobility of the lipoprotein fractions to vary widely with the ionic composition of the buffer. Klotz (3) stressed that the tendency of the 7-globulin fractions to associate with anions is negligible when compared with that of albumin. The ion-binding capacity of other plasma proteins has received but little attention. The influence of cations other than the alkali metals on the electrophoretic mobility of plasma proteins seems to have been neglected (6). The high and relatively selective interaction between inorganic cations and various plasma proteins have been funda-mentally elucidated by the Cohn group (7, 8). They based one of their fractionation schemes on the selective cation-protein interaction. The influence of specific ions and of buffer concentration gradients on the electrophoretic protein fractionation is stressed in this paper. In this respect electrophoresis in a filter-paper medium offers better possibili-ties than moving-boundary electrophoresis, where the salt gradients in the separation system disturb the recording of the protein components