Pyridoxyl-5-phosphate-lysozyme: Physical studies

Abstract

1. 1. Pyridoxal-5- P reacts specifically with lysine residues of lysozyme in 0.1 M phosphate buffer (pH 7.4) at 30°. The activity profile of pyridoxyl-5- P-lysozyme resembles that of the native enzyme at pH values below 6, but it is only 50% as active as native lysozyme at pH values above 7.2. The lysis of cell walls of Micrococcus lysodeikticus by pyridoxyl-5- P-lysozyme is very sensitive to small changes in the ionic strength of the solution. 2. 2. The inactivation of pyridoxyl-5- P-lysozyme by increasing the pH or the ionic strength of the solution cannot be correlated with gross conformational changes of the protein. This is demonstrated by physical studies (polarization of fluorescence, fluorescence spectroscopy and light scattering) designed to detect structural changes in the modified enzyme. 3. 3. The effect of pyridoxal-5- P on the activity of lysozyme is explained in terms of a decrease in the overall positive charges of the protein. It is suggested that the positively charged lysine residues are involved in electrostatic interactions with the cell wall.