KINETICS OF MALT a-AMYLASE ACTION* BY SIGMUND SCHWIMMER

The action of cw-amylase on undegraded starch and on dextrins of high molecular weight is roughly 100 times as rapid as its action on the smaller dextrins formed subsequently. The mechanism of this action has been studied in two ways. By kinetic methods, the course and rate of hydrolysis at varying substrate concentrations are determined. Thus Myrback and Johansson (1) calculated the affinities between the varying split-products and the enzyme from a study of the course of hydrolysis at different substrate concentrations. Similarly Bernfeld and Studer-P&ha (2) have investigated the rate of action of various cr-amylases on amylopectin at varying substrate concentrations. Alternatively, the reaction can be stopped at different stages and the products characterized as to chain length, structure, and subsequent capacity for hydrolysis. Myrblick and Lunden (3) have made a substantial contribution with this approach. More recent studies include that of Alfin and Caldwell (4) on the digestion products of pancreatic amylase action on potato starch and on corn amylose. Swanson has recently characterized the products of action of salivary amylase on glycogen and on amylose (5). Perhaps the current view of the whole case has been succinctly expressed by Myrbllck (6) that cr-amylase “can attack substantially all normal glucosidic linkages in a chain molecule with velocities varying with the distance of the linkage in question from the end-groups.” Three phases of the action of crystallized malt cr-amylase (7) are considered in this report: (a) the ultimate extent of the hydrolysis of starch, (b) the change in the velocity of hydrolysis with increasing substrate concentrations for a variety of substrates other than starch, and (c) inhibition by products of the reaction. It has been found that cu-amylase will ultimately hydrolyze 50 per cent of the glucosidic bonds, with maltose, glucose, and apparently trisaccharides as end-products. Calculation according to classical enzyme kinetics indicates that, for all substrates with chains more than 10 glucose units long, the affinity constant K is invariant within experiment.al limits. The amyloses are hydrolyzed at about double the maximum rate of the amylopectins. Results of the inhibition studies