DENATURATION AND INACTIVATION OF ENZYME PROTEINS

II. DENATURATION AND INACTIVATION OF BACTERIAL AMYLASE

抄録

Inactivation and denaturation of two crystalline bacterial α-amylases (BAN' and BAH) were investigated by assaying the enzymatic activity and determining denaturation by the proteolytic method, at the same time in the case of heat and urea treatment. The “ratio of inactivation” (RI) and the “ratio of denaturation” (RD) of BAN' agreed well, when the amylase was partially inactivated by the foregoing three treatments. Above two ratios, RI and RD, of another bacterial amylase (BAH) also agreed well at every stage during heat and urea treatments. Therefore, it was concluded that the inactivation of all kinds of α-amylases from B. subtilis by the above three treatments must arise not from a special change in the essential radical (or part) of the enzyme molecule but from the alteration of intramolecular structure as a whole. Inactivation of a bacterial amylase by urea treatment was much influenced by the concentration of urea and by temperature, but it was practically uninfluenced by pH in neutral or slightly alkaline solution.
The bacterial α-amylase was strongly protected by calcium ion from inactivation and denaturation by heat, acid, and urea treatments as in the case of other a-amylases. Since the “RI” and “RD” of the amylase agreed well at every stage in the urea treatment, even in a solution protected by the presence of calcium ion, it was supposed that the protective effect of calcium ion on all α-amylases is derived from the protection of a common (or very similar) part in the molecule of all α-amylases which is very important in maintaining the whole secondary structure of the molecule. The bacterial amylase was also protected by the presence of digestion products of starch, from both inactivation and denaturation to the same degree during urea treatment, though the magnitude of the protection was not large.