Preparation of Highly Active Yeast Invertase*

In some preliminary experiments it was found that certain yeast invertase preparations which had been variously purified by adsorption to kaolin and alumina in accordance with the Willstiitter procedures (1) were soluble in saturated aqueous solutions of ammoniym sulfate. This solubility of the enzyme is interesting for two reasons. In the first place, saturated aqueous solution of ammonium sulfate is regarded as almost a universal agent for precipitating enzymes from their aqueous solutions, and in the second place, because saturated ammonium sulfate solutions precipitate practically all proteins so far tried. In other words, this peculiar behavior of the invertase brings up t.he question whether it contains an unusual protein, soluble in saturated aqueous solutions of ammonium sulfate, or whether it contains any protein at all. It seemed even more remarkable, when it was noticed that several other yeast invertase preparations, made in a similar manner, were almost entirely insoluble in this same reagent. This inconsistency was disconcerting until it was noticed that after the removal of the ammonium sulfate by dialysis, the soluble preparations were more active than before the ammonium sulfate treatment (2). Because the autolytic processes by which the invertase preparations are rendered soluble in water consist of a degradation of substances constituting the yeast cell, by other enzymes present in the yeast (3, 4), it was suspected that the variations in the solubilities in saturated solutions of ammonium sulfate manifested