Hydrolysis of Maltose by Taka-amylase A
1968 Volume 63 Issue 5 Pages 632-636
Details
1968 Volume 63 Issue 5 Pages 632-636
1. Maltose was found to be hydrolyzed at pH 5.3 and 25°C by Taka-amylase A [EC 3.2.1.1] preparation which was crystallized three times and which was proved to be of single protein component by electrophoretic and ultra centrifugal analyses.
2. The Michaelis constant Km for the hydrolysis of maltose was found to be numerically equal to the competitive inhibitor constant Ki of maltose for the hydrolysis of p-nitrophenyl α-maltoside catalyzed by Taka-amylase A.
3. This Km value for maltose is one hundred times larger than the Km value for the hydrolysis of maltose catalyzed by Taka-maltase [EC3.2.1.20] or Taka-amylase B [EC 3.2.1.3] preparation.
4. A treatment of Taka-maltase at pH 8.8 and 37°C for 2 hr decreases its specific activity towards maltose, but the same treatment of the crystalline Taka-amylase A preparation causes no loss of specific activity towards maltose. On the other hand, a treatment with 1% HgCl2 solution at pH 6.8 and room temperature for 24 hr for crystalline Taka-amylase A preparation decreases its specific activity towards maltose, but the same treatment for Taka-amylase B causes no loss of specific activity towards maltose.
5. From the results, it was concluded that the observed hydrolysis of maltose was caused by the action of Taka-amylase A itself and not by Taka-maltase or Taka-amylase B which might be contaminated in the crystalline preparation of Taka-amylase A.
6. The Michaelis constant Km for the hydrolysis of maltose catalyzed by Taka-amylase A was determined to be 9.6 ×10-2 M and its breakdown rate constant k+2 of ES complex was determined to be 0.019 sec-1.
