Abstract
I. The velocity constant for dissociation, km, was determined from sedimentation velocity measurements by slightly modifying and directly applying the theoretical equa-tions, and was found to be 1×10-4 mole/liter-sec. The association velocity constant, kD, could be calculated from the association constant as K=2.2×109 (mole/liter)-2, (given by the sedimentation equilibrium measure-ments) and the dissociation velocity constant, and was found to be 2×105 mole/liter. sec.
2. In the previous papers, it was reported that the monomer cf B. α-amylase scarcely exists at concentrations above 0.4 percent protein. Using a synthetic boundary cell, a stable artificial boundary could be created by layering a solution of 0.504 per cent protein over the 1.07 per cent protein solution. The artificial boundary which was formed between the 0.504 ands 1.07 per cent solutions indicated the existance of the dimer alone, while the natural boundary which was somewhat skewed at the trailing edge was suggested to dissociate partly into monomer owing to decrease in the B. α-amylase con-centration to below 0.4 per cent.
The authors wish to express their gratitude to Dr. Shoichi Ikeda for valuable discussion and also their thanks to the Daiwa Kasei Co., Ltd., for supplying Bacillus sublilis α-amylase.
