THE SURFACE-ACTIVITY OF ALPHA-LACTALBUMIN, BETA-LACTOGLOBULIN, AND BOVINE SERUM-ALBUMIN .1. SURFACE-TENSION MEASUREMENTS WITH SINGLE-COMPONENT AND MIXED-SOLUTIONS

The concentration dependence of surface tension was evaluated with DuNoüy ring tensiometry for solutions of α-lactalbumin (α-Lac), β-lactoglobulin (β-Lg), and bovine serum albumin (BSA). Surface tension kinetics were measured as well and interpreted in terms of first-order rate constants defining adsorption and interfacial rearrangement. Although molecularly dissimilar in several ways, the surface activity of each protein could be explained with reference to its relative flexibility and stability. Molecular size seemed to be an important factor governing incorporation of protein into an interfacial layer. α-Lac, the smallest and least stable protein, was observed to be the most surface active. BSA is the largest molecule and consists of three large domains and nine subdomains. Its surface activity is consistent with the thought that it is largely governed by the behavior of one of these domains and its activity after adsorption. β-Lg is roughly half the size of BSA and apparently adsorbs faster than BSA, but exhibited a similar equilibrium II behavior. This is attributed to its dimer structure and the presence of a free thiol in each monomeric subunit capable of facilitating thiol-disulfide interchange reactions, probably causing it to be less flexible than BSA. © 1992.