Binding of calcium to lysozyme and its derivatives

Bindings of calcium to lysozyme and its derivatives were studied by UV difference spectroscopy at various pH's. The binding constant was ca. 40 m-1 at around neutral pH. The binding caused proton release from lysozyme and did not inhibit the binding of tri-N-acetylglucosamine to lysozyme. In the presence of 0.2 M Ca2+, lysozyme showed 26% of the activity of the free enzyme toward hexa-N-acetylglucosamine but the cleavage pattern was similar to that of the free enzyme. Thus, calcium was predicted to bind near the catalytic carboxyls to cause inhibition of lysozyme activity. It was found from the results of protease digestion that calcium binding shifted the native-denatured transition in lysozyme toward the native state.