Influence of pH and ionic strength on the lysis of Micrococcus lysodeikticus cells by six human and four avian lysozymes

Abstract

1. 1. The activities of six human and four avian lysozymes (mucopeptide N- acetylmuramylhydrolase , EC 3.2.1.17) on cell suspensions of Micrococcus lysodeikticus have been examined as a function of ionic strength and pH: three-dimensional models were built. 2. 2. Alkaline pH improves the rate of lysis at low ionic strength for all the lysozymes, with the exception of the goose enzyme. 3. 3. The affinity of the various lysozymes for the substrate is independent of the ionic strength. The variations of pK a,app as a function of pH suggest an analogy of the chemical groups involved in the catalytic mechanism. 4. 4. The percentage of inhibition of all the enzymes by N- acetylglucosamine is a function of pH, but not of ionic strength; it is particularly marked at alkaline pH where the rate of lysis is the highest. 5. 5. Goose egg white lysozyme has a particular behaviour; the maximum activity occurs at acidic pHs (3.8 and 5.25) and at a higher ionic strength than for other lysozymes; the inhibition by N- acetylglucosamine remains very low.