Human lysozyme-catalyzed reaction of chitooligosaccharides.

The time-courses of the human lysozyme-catalyzed reaction of chitopentaose were measured by high-performance gel-filtration in comparison with those of hen egg-white lysozyme. Human lysozyme has considerably larger rate constants for the cleavage of glycosidic linkages and transglycosylation than those of hen lysozyme, in agreement with the fact that human lysozyme exhibits a large lytic activity. It has been reported that binding subsite D in human lysozyme has negative free energy on substrate binding, whereas subsite D in hen lysozyme has unfavorable positive free energy due to the distortion of a sugar residue. The time-courses calculated under the assumption that subsite D in human lysozyme has negative free energy on substrate binding did not fit the experimentally obtained time-courses, even though the combination of values of rate constants in the enzymatic reaction widely varied in the calculation of the time-courses. Thus, it was concluded that subsite D in human lysozyme may not have negative binding free energy, but positive values similar to hen lysozyme.