Kinetic Studies on Gluc-amylase
IV. Hydrolysis of Isomaltose
1966 Volume 59 Issue 5 Pages 476-480
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1966 Volume 59 Issue 5 Pages 476-480
1. The Michaelis constant Km and the maximal velocity V have been determined for the hydrolytic reaction of isomaltose catalyzed by crystalline glut-amylase of Rh. delemer at 25°C and pH 5.1.
2. It has been found that isomaltose acts as a competitive inhibitor to the hydrolytic reaction of panose catalyzed by this enzyme, and the inhibitor constant of isomaltose Ki is equal to the Michaelis constant Km of isomaltose as substrate.
3. From the study of the influence of pH on the rate of hydrolysis of isomaltose at substrate concentration sufficiently lower than its Km value, the pKe values of the essential ionizable groups of the free enzyme involved in the hydrolysis of isomaltose have been determined to be pKe1=2.85 and pKe2=5.85, which are in good agreement with those obtained for maltose and panose as substrate.
4. The above results have confirmed that the active center of the enzyme involved in the catalytic hydrolysis of isomaltose is the same as that involved in the hydrolysis of maltose and Danose, and that both α-1, 4 and α-1, 6 glucosidic linkages are hydrolyzed by the same active center of the enzyme.
The authors gratefully acknowledge the kindness of Professor J. Fukumoto and Dr. Y. Tsujisaka of Osaka Municipal Technical Research Institute who provided the crystalline enzyme and of Professor K. Shibasaki who furnished isomaltose and panose.
