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 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 degree of O-acetylation. The steady-state parameters, Km 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 Km 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#)], a consequence of increasing O-acetylation, was observed, and is shown to result from the weaker affinity of the enzyme for the modified substrates.
Dupont
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Guelph-Waterloo Centre for Graduate Work in Chemistry, Department of Microbiology, University of Guelph, Ontario, Canada.
Clarke
A J
AJ
D000107:Acetylation; D007202:Indicators and Reagents; D007700:Kinetics; D009113:Muramidase / Q000378:metabolism*; D010457:Peptidoglycan / Q000737:chemistry* / Q000302:isolation & purification; D011513:Proteus mirabilis / Q000032:analysis*; D012995:Solubility; D013045:Species Specificity
D007202:Indicators and Reagents; D010457:Peptidoglycan; D009113:Muramidase