Substituent effect on lysozyme-catalysed hydrolysis of some β-aryl di-N-acetylchitobiosides

Abstract

Measurements are reported on the kinetics of the lysozyme-catalysed hydrolysis of several beta-aryl di-N-acetylchitobiosides, some of which have been synthesized for the first time. The catalytic rate constants (k(cat.)) at 45 degrees yield a curved Hammett plot (concave up) and the plot of DeltaH(double dagger) versus DeltaS(double dagger) has a sharp break. Substrates with electron-withdrawing groups exhibit a kinetic deuterium isotope effect (k(H) (cat.)/k(D) (cat.)), whereas those with electron-donating groups show no such isotope effect. The results suggest the operation of different mechanisms for the two types of substrates.

Nucleophilic Competition in Some β‐Galactosidase‐Catalyzed Reactions

“…There is no correlation between the enzymatic hydrolysis rate and the chemical reactivity of the substrates expressed by the 0 parameter according to the Hammet equation. Such a situation has been observed with other glycosidases [15,16].…”

“…Such a behaviour has already been reported for other glycosidases [15,16]. phenyl galactoside, there is no effect of methanol (Fig.4); the limiting step is the formation of ES', which is different from the behaviour of this substrate in the presence of magnesium.…”

Hydrolysis ofpara-Substituted Phenyl-β-D-xylosides by β-Xylosidase fromMalbranchea pulchellavar.sulfureaNo. 48

“…A similar observation for other glycosidases has been reported. 7 ,9,10) Tsai et al 7 ) investigated the hydrolysis of a series of parasubstituted fJ-phenyl-di-N-acetyl-citobiosides by lysozyme, obtained concave Hammett constant relationship with p = +0.55…”

X‐ray structure of glu 53 human lysozyme

“…If such nonproductive binding dominates the complex formation, the kc,, value for the hydrolysis of oligosaccharides could be decreased despite having a similar K,,, value. A reaction mechanism involving the formation of the enzyme-substrate covalent bond has also been discussed (Tsai et al, 1969;Craze et al, 1978). In this case, the carboxyl group of residue 53 should be located at such a position that it can attack the C-l carbon atom of the substrate.…”