Lysozyme mechanism, acylal intermediate

The lysozyme mechanism (Scheme 11.21) has an acylal intermediate with a decay step which is fast compared with its rate of formation, so it is not normally possible to observe the intermediate. The acylal mechanism has recently been established by modifying both enzyme and substrate so that the intermediate can be isolated in this case, the intermediate was stabilised so much that its X-ray crystallographic structure could be determined. Substrate A in Scheme 11.21 was employed [22 ] in which the 2 -fluoro substituent reduces the reactivity at the Cl position so that any acylal enzyme formed from this substrate would have a... 

Scheme 11.21 Lysozyme mechanism for hydrolysis of the substrate jS-cel lob iosyl fluoride A is a modified reactive substrate which yields a weakly reactive acylal intermediate.

Studies of the stereochemical course of the transglycylation reactions catalysed by lysozyme show retention of configuration at Cl in the product. This can be attributed most economically to the intervention of an acylal intermediate in the mechanism (see Scheme 11.21). A similar result is found in the alkaline phosphatase-catalysed solvolysis of isotopomeric phospho-esters which indicates a double inversion via a phospho-enzyme intermediate (Scheme 11.22). 

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