Inhibition of glycosidases by aldonolactones of corresponding configuration. 2. Inhibitors of β-N-acetylglucosaminidase

Abstract

Conchie & Levvy (1957) found that, in general, the enzymic hydrolysis of a simple glycoside was in- hibited by the aldonolactone corresponding in configuration to the sugar residue of the substrate.This suggested that the structural requirements necessary for a specific inhibitor of fl-N-acetylglucosaminidase would be fulfilled by the com- pound 2-acetamido-2-deoxygluconolactone (N- acetylglucosaminonolactone).Hitherto the most effective competitive inhibitor of this enzyme has been the hydrolysis product, N-acetylglucosamine, which has a considerably lower affinity than the substrates customarily used for assay (Pugh, Leaback & Walker, 1957b).N-Acetylglucosaminonolactone has not pre- viously been synthesized, although Hope & Kent (1955) stated that the crude product of the treatment of glucosaminic acid with keten had the characteristics of a lactone.Partial acetylation of glucosaminic acid with acetic anhydride yielded a product, which, while not crystalline, possessed the properties of the required compound.Another obvious route was by selective oxidation of N- acetylglucosamine, and this was performed success- fully by two different methods.As was expected, N-acetylglucosaminonolactone proved a potent inhibitor of f-N-acetylglucosaminidase.Ram testis and emulsin preparations with ,B-Nacetylglucosaminidase activity have been shown to hydrolyse p-nitrophenyl N-acetyl-fp-D-galactosaminide, and it has been tentatively concluded that the glucosaminidase is responsible (Heyworth, Borooah & Leaback, 1957).If this is so, 2-acetamido-2-de- oxygalactonolactone (N-acetylgalactosaminonolactone) would also be expected to inhibit the enzymic hydrolysis of N-acetyl-fl-D-glucosaminides; this has been found to occur.The complex structural changes in the inhibitory lactones under varying conditions of pH have been studied, largely by changes in their inhibitory power.For most experiments, preparations of adult rat epididymis were used, since this tissue was found by Conchie, Findlay & Levvy (1956) to have much greater fl-N-acetylglucosaminidase activity than * The paper by Conchie & Levvy (1957) is to be regarded as Part 1.