Characterization of Enzyme-substrate Complex of Lysozyme

II. Effects of pH and Salts

Abstract

The effects of pH and salts on the activity of lysozyme [EC 3. 2. 1. 17] and the formation of the enzyme-substrate complex were studied spectrophotometrically and by chromatography on a column of an insoluble substrate, carboxymethyl (CM) chitin. The activity of lysozyme was strongly inhibited by neutral salts at high concentrations. In contrast, the formation of the enzyme-substrate complex measured by difference spectrophotometry and chromatography on CM-chitin column increased on increasing the salt concentration. The effect of salts (ions) on the activity depended upon their ionic radii. These effects of salts could not be explained merely by their influence on the ionization of amino acid side chains of the lysozyme molecule. The effects of salts on the complex formation and the activity, therefore, seemed to be mediated by a fine conformational change at the active site, resulting in an unsuitable arrangement of catalytic groups for the catalytic reaction and a strong interaction between the lysozyme molecule and the substrate.