Studies on enzyme action. XII.-The enzymes of emulsin

Abstract

Emulsin has frequently been the subject of discussion in this series of studies: thus the rate at which it hydrolyses milk-sugar was considered in No. II (Vol. 73, pp. 507, 515) and its action contrasted with that of Kephirlactase, which was shown to act more rapidly than emulsin. In No. III (vol. 73, p. 518) it was pointed out that whilst Kephir-lactase is controlled by galactose and scarcely at all by galactose. These conclusions were confirmed by experiment with the methyl-glucosides and galactosides (p.523). In No. V (Vol. 74, p. 188) the question was discussed whether emulsin proper hydrolyses milk-sugar or whether, as Bourquelot and Hérissey have contended, emulsin contains a small proportion of lactase: against this assumption it was argued that the curve was not of the form to be expected if only a small quantity of lactase were present; that whereas Kephir-lactase was controlled by galactose alone, emulsin was most retarded by glucose and only to a slight extent by galactose, also that the curves for emulsin differed in character from those for lactase. Attention was directed, however, to Pottevin’s statement that Aspergillus niger contains an enzyme capable of hydrolysing β -glucosides, but not β -galactosides nor milk-sugar. In No.X (B, vol. 79, p. 360) some of the statements made in earlier studies were rectified and it was announced that evidence had been obtained, to the presence of a distinct enzyme capable of hydrolysing only β -glucosides. While admitting this to be the case, however, we may point out that the conclusions we have to bring forward involve merely a different reading of the facts: the facts have been correctly advanced on both sides.