Effect of Salts on the Thiol-dependent Gelation of Bovine Serum Albumin

Abstract

A previous report [M. Hirose, Y. Nishizawa and J. Y. Lee, J. Food Sci., 55, 915 (1990)] has shown that the thio-dependent gelation of bovine serum albumin was strongly inhibited by high concentrations of salts. The inhibition mechanism was investigated in relation to the conformation and disulfide cleavage of the protein. The effects on the thiol-dependent disulfide cleavage of the protein varied with the salt species, especially with the anion species. The circular dichroism spectra and difference UV-spectra showed that anions induced some conformational changes in the tertiary structure, but not in the secondary structure. With regard to a chaotropic anion, perchlorate, this conformational change was closely correlated with the inhibition of gelation and disulfide reduction. In contrast, a lyotropic anion such as sulfate inhibited the gelation at a higher concentration than the concentrations that induced the conformational change. In addition, this anion showed no inhibition effect on disulfide reduction. Thus, we conclude that there are two inhibition sites for the thiol-dependent gelation of BSA. One involves the reductive cleavage of disulfide bonds, and the other probably concerns intermolecular interaction of the disulfide-reduced protein. © 1991, Japan Society for Bioscience, Biotechnology, and Agrochemistry. All rights reserved.