The Activation Energy of Urea Hydrolysis Catalyzed by Soy Bean Urease

The rate of most chemical reactions increases exponentially with temperature in accordance with the Arrhenius equation. The older literature on enzyme-catalyzed reactions (for references cf. Haldane (1930), Tauber (1937)) indicates that these do not. conform, since the activation energy decreases with rise in temperature instead of being invariant. More recent studies do not confirm this general statement, however, but indicate that the reaction velocity of certain enzyme systems increases with temperature in conformity with the Arrhenius equation up to the inactivation temperature of the enzyme (Bodansky, 1939; Craig, 1936; Crozier, 1924; Gould and Sizer, 1938; Hadidian and Hoagland, 1939; Sizer, 1937, 1938, 1939). Bodansky (1937) has emphasized the fact that in much of the earlier work little attention was paid to pH control, and velocity constants were often improperly computed. A comparison of the activation energies of catalytic systems in which the enzyme has been obtained from different species can yield valuable information concerning the biochemical relationships of enzymes. Sizer (1937) reported an activation energy of 13,000 calories per gm. mole for sucrose hydrolysis by malt invertase as compared with 11,000 calories for yeast invertase (1938). Bodansky (1939), on the other hand, obtained a value of 9940 calories for the hydrolysis of sodium ,&glycerophosphate by either human or cat bone phosphatase. Activation energies of either 8700 or 11,700 calories were reported (Sizer, 1939) for urea hydrol-