Association and Dissociation of <i>Bacillus subtilis</i> α-Amylase Molecule:II. Studies on Monomer-Dimer Transformation by Gel Filtration

1) The studies on monomer-dimer trans-formation of Bacillus subtilis α-amylase mole-cule were made by measuring the sedimen-tation velocities as well as by the dextran gel filtration (Sephadex G-100). The results obtained in either case was the same and the following scheme: 2 Monomer +Zn²⁺_??_Dimer, is hold in the present experimental conditions.<br> 2) The elution diagrams and the sedi-mentation patterns were varied with the concentration of B. α-amylase, that is, at the high concentration the faster moving com-ponent corresponded to dimer form, 6.2S, whereas the slower moving component mono-mer form, 4.4 S. At the lower concentration only a single peak was observed.<br> 3) The following conclusion was deduced from the elution diagrams varied with the elution rate and the quantitative analysis of zinc ion contained in the effluent. The rate of the equilibration between monomer and dimer was equal to the flow rate of the gel filtration in the present experimental con-ditions.<br> 4) The ultracentrifugal experiments were carried out in the wide range of the concentration of B. α-amylase. At the concen-tration of less than 0.1 per cent s_20w dec-reased sharply from 6. 2 S to 4. 4 S and also the sedimentation patterns showed a single peak.<br> 5) As evidenced from the present investi-gation the enzyme should be in the mono-mer form under the experimental conditions assaying the enzymatic activity. As can be seen in Table II, the enzymatic activity was unchanged in the presence of high concen-tration of zinc ion. Accordingly, it might not be affected by the change of monomer-dimer transformation. The authors would like to express their thanks to Daiwa Kasei Co., Ltd. for supplying Bacillus subtilis α-amylase.