Sucrase

SUCRASE (invertin), an enzyme that splits sucrose into d-glucose and d-fructose and gentianose (hexitriose) into d-fructose and gentiobiose (β-glycosido-6-glucose). It is extremely widespread in various types of yeasts and other cryptogamous and higher plants; in the animal organism it is found in the mucous membrane of the small intestine, and probably also in intestinal juice and leukocytes; it is absent in the intestinal juice of ox and pig fetus; it appears in the blood only as a protective enzyme in young animals when sucrose is injected into the blood. S. was isolated in crystalline form by Willstätter. By type of action, S. is a fructosucrase, with the exception of S. from Asperg. Oryzae, which belongs to glucosucrases (Kuhn). From living and healthy yeast cells, S. is not secreted outward; the formation of S. depends on the nutrition of the cell; the addition of sugar stimulates its formation. The optimum for human sucrase lies at pH 5-7, for pig at pH 4.75, and for yeast sucrase at pH 3.5-5.5. S. is very sensitive to changes in pH toward alkalinity. Neutral salts, alkaline salts, and FeSO₄ have no effect on S. purified from protein; heavy metals have a reversible inhibitory effect. Ethyl alcohol has no effect on S. (?), methyl alcohol in small concentrations weakens it, and at 60% completely stops the action of S.; acetone, glycerin, and products of sucrose hydrolysis also have an inhibitory effect. The sucrase of intestinal juice is more thermolabile than yeast sucrase: it is inactivated when heated for one hour to 51° and is completely destroyed at 55°. For the detection of sucrase, inversion (see) of sucrose is used, applying polarimetric analysis or observing the appearance of reducing capacity in Trommer's test.