Albumin from heated human plasma. III. Denaturation kinetics: Influence of acetate ions

Abstract

The influence of acetate ions on the denaturation of human plasma albumin has been studied by measuring the reaction rate as a function of pH and temperature. The process of denaturation follows first-order kinetics with respect to protein concentration and also appears to be first order with respect to acetate. At constant acetate-ion concentration, measurements of the change in the experimental rate of denaturation with pH show that the role of the hydrogen ion in the denaturation process is the same as has been previously determined in the absence of acetate. In the presence of acetate, there is an increase in the value of the dissociation constant for the five key prototropic ionizations which control the stability of the protein. However, the effect of temperature on the p K remains unchanged. At 54.9 °, when acetate is present, there is a marked elevation in the rate of the net denaturation reaction, which occurs when albumin becomes labile as a result of the suppression of three of the key dissociations. At 69.6 °, the rate is found to be greater in the absence of acetate. Thus, the heat of activation for the net denaturation reaction is considerably lower when acetate is present.