Lysozyme transition state analogues

Lysozyme catalyzes the hydrolysis of the polysaccharide component of plant cell walls and synthetic polymers of j8(l — 4)-linked units of A-acetylglucosamine (NAG) (Chapter 1). It is expected from studies on nonenzymatic reactions that one of the intermediates in the hydrolytic reaction is a oxocarbenium ion in which the conformation of the glucopyranose ring changes from a full-chair to a sofa (half-chair) conformation (Chapter 1). The transition state analogue I, in which the lactone ring mimics the carbonium ion-like transition state n, binds tightly to lysozyme = 8.3 X 10 8M.10... 

So-called transition state analogues which bind to the enzyme more tightly than natural substrates probably do so not so much because of a geometrical complementarity to the enzyme but more as a result of compatible electrostatic interactions. For example, it seems more likely that lactones (XIX) bind to lysozyme better... 

The association constant for the binding of Gd + ions to lysozyme has been determined at pH 5.2 (by measuring the release of protons) and at pH 6.5 (by u.v. spectroscopy). In agreement with X-ray data, it was found that Gd + ions bind to the carboxy-groups of L-glutamic acid-35 and L-aspartic acid-52 at the junction of sites D and E in the cleft of the enzyme. The association constants for the binding of several inhibitors and substrates to lysozyme and to the complex with Gd + were determined by fluorescence spectroscopy the lactone derived from the tetra-iV-acetylchitotetraose (a transition-state analogue) had a... 

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