抄録
A novel CGTase (Cyclomaltodextrin glucanotransferase) has been isolated from a strain of Thermoanaerobacter, a thermophilic anaerobe. The enzyme is extremely heat stable and has a temperature optimum of 90-95°C at pH 6.0. It is active over a broad pH range, and exhibits more than 80% activity from pH 5.0-6.7. In the presence of starch, the enzyme is stable at temperatures in excess of 100°C. In addition to producing cyclodextrins from starch, Thermoanaerobacter sp. CGTase has excellent starch liquefying properties. It is possible to liquefy a 35% DS starch slurry at pH 4. 5, in the absence of calcium, using the "jet cooker" process developed for B. licheniformis α-amylase (105°C for 5 min, 90-95°C for 90 min). Saccharification of the liquefied starch with A. niger glucoamylase can therefore be carried out without further pH adjustment. Some of the properties of Thermoanaerobacter sp. CGTase are described, and examples of the use of the enzyme for cyclodextrin production, intermolecular transglycosylation and starch liquefaction are given. The gene coding for Thermoanaerobacter sp. CGTase has been transfered to a Bacillus host, making large-scale production of the enzyme in commercially acceptable yields possible.
