Effects of temperature and pH on the regeneration of the amino groups of ovalbumin after modification with citraconic and dimethylmaleic anhydrides

Abstract

The reagents citraconic and dimethylmaleic anhydrides modify the amino groups of proteins in a reversible way, the modified amino groups being regenerated at moderate acid pH. To use these reagents efficiently it is important to know the stabilities of the modified groups under different experimental conditions. We have studied the kinetics of deacylation of ovalbumin amino groups modified with citraconic and dimethylmaleic anhydrides, under different conditions of temperature (0–40°C) and pH (4–8). The deacylation of the modified groups follows pseudo-first-order kinetics under all experimental conditions studied. For both reagents, the dependence of the rate of deacylation on temperature obeys the Arrhenius equation, and the logarithm of the apparent deacylation constant shows a linear dependence on pH. From the experimental data, equations have been obtained for both reagents relating the deacylation constant with temperature and pH. These equations allow the calculation of the deacylation constant and the half-life of the modified groups for any conditions of temperature and pH within the experimental intervals studied.