Zur Kenntnis der Hefeasparaginase.

Abstract

The enzyme is best prepared by autolysis, with a slightly alkaline reaction, in the presence of toluol or (NH4)2SO4. The reaction curve for the splitting of 1-[beta] asparagine is nearly linear. Aminopolypeptidase cannot be separated from asparaginase by autolysis in strongly alkaline solutions as both enzymes are about equally affected by alkali. Asparaginase is preferentially adsorbed by kaolin and by the use of suitable amounts of adsorbent it is possible to obtain about 1/2 of the polypeptidase free from asparaginase while by elution of the adsorbate the asparaginase increases 3-9 times as compared with the aminopolypeptidase but cannot be obtained free from the latter. The removal of the peptidase can be accomplished most easily by means of certain enzyme poisons such as HCN, H2S and pyrophosphate. Thus BUS and pyrophosphate up to a concentration of 1/50 M per 1. produce no definitely measurable inhibition of asparagine splitting while in much lower concentration they completely suppress di- and polypeptidase activity. Asparaginase is, with extraordinarily great specificity, limited to the constitution and configuration of natural l-[beta]-aspara-gine. Even the substitution of an amino group of the asparagine by an acid radical or by an amino acid is sufficient to retard the splitting of the amide linkage. Glutamine, at least in the presence of Na pyrophosphate, is not decomposable, even by highly active asparaginase. The existence of a glutamine-splitting enzyme with asparaginase appears probable but needs further confirmation. The experiments performed lead to the conclusion that the asparaginase activity is associated with the presence of a [long dash] CO.CH2CH2 [long dash]CONH2 grouping in NH2 the substratum. Asparaginase is able to act on a substratum only if this group lies free at least with reference to its amino group.