Lysozyme-catalysed hydrolysis of some beta-aryl di-N-acetylchitobiosides.
1. Four beta-aryl di-N-acetylchitobiosides and beta-S-phenyl di-N-acetylthiochitobioside have been prepared and shown to be substrates for hen's-egg-white lysozyme. 2. The lysozyme-catalysed hydrolysis of these substrates obeys Michaelis-Menten kinetics. 3. The Michaelis constants, K(m), for the beta-aryl di-N-acetyl-chitobiosides are almost independent of the aglycone, whereas the catalytic constants, k(cat.), show a marked dependence, giving a Hammett reaction constant, rho, equal to 1.2; this suggests the rate-determining step involves concerted acid-base or acid-nucleophilic catalysis. 4. This conclusion is supported by the Michaelis-Menten constants found for beta-S-phenyl di-N-acetylthiochitobioside. 5. A three-step reaction pathway is proposed, and mechanisms are suggested that would account for the evidence currently available.
D000818:Animals; D001665:Binding Sites; D002384:Catalysis; D002645:Chickens; D002686:Chitin / Q000378:metabolism; D003445:Crustacea; D006027:Glycosides / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008956:Models, Chemical; D009113:Muramidase / Q000378:metabolism*; D010047:Ovalbumin; D011134:Polysaccharides / Q000138:chemical synthesis / Q000378:metabolism*
D006027:Glycosides; D011134:Polysaccharides; D002686:Chitin; D010047:Ovalbumin; D009113:Muramidase