UNIFORMITY IN INVERTASE ACTION
Journal of the American Chemical Society
The study of the nature of enzymes has developed chiefly along two distinct lines. So far all attempts to isolate an enzyme as a pure substance of definite chemical composition have been without satisfactory results. Accordingly considerable work has been done to gain an insight into the nature of the enzyme itself by studying the velocity of the reaction which is catalyzed by the enzyme. The object in all these researches on the chemical kinetics of enzyme action has been to find some general
... find some general law governing the rate of the reaction, and by means of this to make deductions concerning the mechanism of the action and the nature of the enzyme. Xn all such work the tacit assumption has been made that any two preparations of the same enzyme. if the same amount of active enzyme is present, .and other conditions are the same, will catalyze the reaction a t identical rates at corresponding points throughout. In other'words, if the course of the reaction were plotted, the two curves should be superimposable, While this assumption has not been definitely stated in the past, it is a necessary implication of the attempt to find a general law for the rate of the catalyzed reaction. Accordingly it seemed desirable, before going further in the attempt to obtain a general law for the hydrolysis of cane sugar by the catalytic action of invertase, to find out by direct experiment whether several different enzyme preparations would really give the same quantitative course to the reaction. 11. Differences in Invertase Action. In order to make this comparison, it was necessary to have all the conditions alike except for the use of different invertase preparations. The conditions adopted were a temperature of 25", an initial sucrose concentration of 10 g. per 100 cc., and a hydrogen-ion concentration of 1 0 -4 4 to 10-4.6 secured by 0.01 M buffer solution of acetic acid and sodium acetate. The amounts of invertase were so adjusted in each experiment that the reaction started off a t the same rate. This was accomplished by a few preliminary experiments, making use of the fact noted by Nelson and Vosburgh,I that the velocity of inversion is directly proportional to the concentration of the enzyme. The extent of inversion was determined by the polariscopic method. That this method is justifiable has been established by Vosburgh2.