Microheterogeneity of human serum albumin: evidence for differences in reducibility of disulfide linkages

Studies were designed to determine the causes of the microheterogeneity of human serum albumin. Human serum albumin in 3 M KCl was fractionated in a stepwise manner by lowering the pH. The resultant fractions showed similarities in: (a) the reactivity of ε-amino groups with trinitrobenzenesulfonic acid, (b) the binding of sodium dodecyl sulfate to the free amino groups, and (c) the ability to precipitate with anti-human serum albumin. Conversely, differences existed in the susceptibility to reduction of disulfide bonds of the various fractions with β-mercaptoethanol, which suggested that the microheterogeneity of human serum albumin and its fraction may be due, in part at least, to differences in the pairing of the disulfide bonds.