Activation of pepsin (EC 3.4.4.1) by heavy-metal ions including a contribution to the mode of action of copper sulphate in pig nutrition.

Abstract

1. Kinetic experimetns were done with pepsin (EC 3.4.4.1) using haemoglobin as a substrate in the presence of different metal cations. 2. The activation of peptic hydrolysis with higher concentration of cupric ions added to the reaction mixture was determined from turnover-rate curves in experiments with constant substrate concentration. With a Cu2+ concentration greater than 1.67 X 10(-4) M activation was obtained. 3. Nickel ions at a concentration of 8-33 X 10(-4) M and at higher concentrations also increased pepsin activity. Additions of ferrous ions and zinc ions had no effect. 4. Experiments were done using variable substrate concentrations in the presence of different Cu2+ concentrations. The concentrations of haemoglobin ([S]) at half maximum velocity were determined. The double-reciprocal plots of [S] v. reaction velocity (v) (i.e. 1/[S] v. 1/v) had no common intersection point. Therefore the kinetics did not correspond to any of the known kinetics. The activation brought about by Cu2+ cannot easily be explained by the study of the kinetics. Certain simple explanations of the phenomenon can be eliminated.