The Extracellular α-Amylase of Bacillus stearothermophilus

Abstract

During the course of an investigation of the synthesis and secretion of bacterial extracellular enzymes, Bacillus stearothermophilus α-amylase was found to be different from that previously described. Repetition of the purification procedure for the enzyme yielded crystals which were identical in appearance with those reported to be B. stearothermophilus α-amylase, but which are not in fact the enzyme. A new purification procedure for the enzyme has been devised. The purified enzyme was found to have properties different from the unique ones previously described for B. stearothermophilus α-amylase, but resembled those of other α-amylases. The molecular weight was approximately 53,000, and it also resembled other bacterial extracellular enzymes in lacking cyst(e)ine. Although the enzyme was capable of hydrolyzing starch at temperatures of 70° and above, it did not possess unusual thermostability. The enzyme was protected from thermal denaturation above 55° by metal ions, particularly Ca2+, and by protein. The purified B. stearothermophilus enzyme is 50% inactivated in 24 hours at 6° while completely stable at 25°. It is concluded that the enzyme studied here does not have the semi-random coil structure previously reported for an α-amylase produced by B. stearothermophilus.