Über Gluco- und Fructosaccharase II.

Abstract

Hydrolysis of sucrose by yeast saccharase is checked by a-glucose not because of the affinity of the enzyme for this hexose, but because of the reduction of the speed of decomposition or formation of the enzyme-sucrose compound. The dissociation constant of this compound is affected by [beta]-glucose and by fructose, but not by a-glucose. From this it follows that yeast saccharase attacks the fructose half of the sucrose (fructo-sac-charase). This is confirmed by the conduct of derivatives of sucrose, such as hesperonal, raffinose, gentiobiose, and melezitose; yeast saccharase attacks only those derivatives in which the fructose half is intact. Gluco-saccharase is present in other fungi, and attacks only those sucrose derivatives in which the glucose half is intact. These relationships are not changed by culture of the organisms on glucose or fructose. The validity of H. v. Euler''s rule that the dissociation constant of the enzyme-sucrose compound equals the product of the dissociation constants of the enzyme-glucose and enzyme-fructose compounds is negated.