The hydrolysis of glucosaminides by an enzyme in Helix pomatia.

IT has long been known that the polysaccharide chitin when completely hydrolysed yields glucosamine and acetic acid; in recent years it has indeed been shown conclusively that the basic unit of the polysaccharide is N-acetylglucosamine. The evidence for the latter statement rests, firstly, on the discovery by Karrer & Hofmann [1929] ofan enzyme in Helixpomatiawhich is able to hydrolyse chitin to N-acetylglucosamine and, secondly, on the isolation of chitobiose octaacetate by Bergmann et al. [1931] and by Zechmeister & Toth [1931] as a product of acetolysis of chitin. In view of the conclusions which have been reached concerning the structure of polysaccharides from experiments on their hydrolysis by enzymes possessing ccor fl-specificity, it was thought that an enzyme such as that discovered by Karrer might, if it could be characterized, be used to investigate the stereochemical structure not only of chitin itself but of other glucosamine-containing polysaccharides such as that of egg albumin [Neuberger, 1938]. For this purpose it was clearly necessary to determine the acor fl-specificity of the enzyme before any conclusions could be reached as to the configuration of the natural linkages in such polysaccharides, and it was also thought desirable to investigate other factors which might influence enzyme action, such as variations in the N-acyl group and substitution on carbon atoms other than C1. Up to the present, little has been known about the specificity of chitinsplitting enzymes. Zechmeister and his co-workers [1932] found that emulsin contains an enzyme capable of hydrolysing chitodextrin, a product obtained by partial acid hydrolysis of chitin. It was first presumed by these authors that the enzyme responsible for hydrolysis was the glucosidase in emulsin which is known to possess fl-specificity, and they therefore concluded that chitodextrin and chitin have a fl-structure. The assumption they made was shown to be incorrect by Helferich & Iloff [1933], who found that fi-glucosidase and chitinase were different enzymes. Later, Zechmeister and his co-workers [1934] confirmed Helferich's observation, by demonstrating that a highly purified sample of fi-glucosidase is inactive towards chitin. With regard to the N-acyl specificity of the enzyme, some preliminary experiments were done by Karrer & White [1930]; these authors treated chitin with strong alkali and obtained a poorly characterized but presumably partly deacetylated product, chitosan, which, on enzymic hydrolysis, yielded a mixture. If, however, the chitosan were reacetylated, the product of enzymic hydrolysis was pure N-acetylglucosamine. Products purporting to be N-formyl, N-propionyl, N-butyryl and N-benzoyl derivatives of chitosan were also prepared, of which the only one to be attacked by the enzyme was the N-benzoyl derivative, and that to only a small extent. These experiments suggest that the enzyme will