Effect of substituents on the hydrolysis of substituted phenyl .BETA.-acetylglucosaminides by bovine liver .BETA.-acetylglucosaminidase.

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Abstract
Km and relative catalytic constant, .**GRAPHIC**. were determined for the .beta.-acetylglucosaminidase-catalyzed hydrolysis of a series of substituted phenyl .beta.-acetylglucosaminides; the substiuents are 2,4-dinitro, p-nitro, 4-nitro-3-methyl, m-nitro, p-chloro, m-chloro, p-methyl, m-methyl, p-methoxy and p-hydroxyl groups. The values were evaluated in terms of the .rho.-.sigma. relationship of Hammett. Plots of log Km with respect to Hammett substituent constant, .sigma. and Hansch substituent constant, .pi. showed the enzyme-substrate affinity to be dependent on the electronic nature of the substituents (.rho. = -0.42, correlation coefficient r = 0.943) but not on the hydrophobic nature. The log .**GRAPHIC**. value was only slightly dependent on .sigma. value (.rho. = +0.16, r = 0.626). An experiment on nucleophilic competition with methanol was carried out in an attempt to explain the small .rho. value for .**GRAPHIC**. Methanol competes with water for the glycosyl enzyme to some extent but does not increase .**GRAPHIC**. for the glycosides examined, indicating that the deglycosylation is not rate-limiting and the .rho. value for .**GRAPHIC**. pertains to the reaction of glycoside bond cleavage.

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