DEPENDENCE OF LYSOZYME-CATALYZED SOLUBILIZATION OF PROTEUS-MIRABILIS PEPTIDOGLYCAN ON THE EXTENT OF O-ACETYLATION

The degree of peptidoglycan O-acetylation in 14 strains of Proteus mirabilis has been accurately determined by a procedure which employs the quantitation of mild-base-released acetic acid by HPLC, and the estimation of peptidoglycan concentration by cation-exchange amino acid analysis. The beta-D-N,6-O-diacetylmuramyl content of all isolated and purified peptidoglycans was ranged 20-52.8%, relative to the total muramic acid concentration. Each of the O-acetylated peptidoglycans was found to be resistant to solubilization by both human and hen egg-white lysozymes and for hen egg-white lysozyme, the extent of this resistance was dependent upon the dependent upon the degree of O-acetylation. The steady-state parameters, K(m) and V, for the hen-egg-white-lysozyme-catalysed solubilization of various peptidoglycan preparations were determined at pH 6.61 and 25-degrees-C. Values of K(m) for the different peptidoglycan samples were found to increase with increasing O-acetylation, whereas with V no such relationship appeared to exist. An increase in the overall change in the standard Gibbs free energy of activation [DELTA(DELTA-G double-ended-dagger)], a consequence of increasing O-acetylation, was observed, and is shown to result from the weaker affinity of the enzyme for the modified substrates.