Bacillus stearothermophilus. I. Thermal and pH stability of the amylase.

Investigators are agreed (Kneen and Sandstedt, 1946; Myrback and Neumuiller, 1950) that bacterial amylases, except crystalline preparations (Meyer et al., 1947; Bernfeld, 1951), possess a greater thermostability than other alpha-amylases. Although many investigators have studied the heat stability of amylases from various sources, no study has been published comparing the thermal resistance of extracellular hydrolytic enzymes from thermophilic and mesophilic bacteria. Conn, Johnson and Miller (1950) tested the temperature of inactivation of a group of alpha-amylases in the amylograph at 60 to 85 C. These investigators found that a mesophilic bacterial amylase, Rhozyme-DX, was more heat stable than amylase preparations from certain other bacterial, malted flour, and fungal sources. Stark and Tetrault (1951) described the isolation of cell-free, starch saccharifying enzymes from the culture medium of Bacillus stearothermophilus ATCC 7954 at 70 C and demonstrated saccharogenic activity at 90 C. Campbell (1952) compared the amylase preparations obtained from both B. stearothermophilus 1518 and B. coagulans 43P grown at 35 and 55 C. He found that the amylases produced at 55 C had a somewhat higher optimum activity temperature (60 to 70 C) than those produced at 35 C (45 to 55 C). When exposed to a temperature of 90 C, the amylases produced at 35 C lost all detectable activity after 2 hours, but the amylases produced at 55 C had retained 50 per cent of their activity for 24 hours. Since thermostability of enzymes is important in some industrial processes and thermophilic bacterial amylases have been shown to be quite heat resistant, a comparative study was made of three commercially available bacterial amylases with a thermophilic bacterial amylase preparation. The pH stability of the thermostable amylase preparation at 60 C was also observed.