Dependence of lysozyme‐catalysed 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 β‐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 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°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 [Δ(Δ G ± )], a consequence of increasing O ‐acetylation, was observed, and is shown to result from the weaker affinity of the enzyme for the modified substrates.