抄録
A thermophilic fungus, Aspergillus K-27, produced extracellular amylolytic enzymes in a submerged culture with wheat starch as a carbon source at 45°C. By adding α-methyl-D-glucoside to the medium as an inducer, the enzyme production was doubled on five days cultivation. The enzymes strongly digested not only cereal but also tuber and root starches without gelatinization. The relative rates of hydrolysis of corn, tapioca, wheat, sweet potato and potato starches were 1.0, 0.91, 0.83, 0.75 and 0.72, respectively.
The crude enzyme fraction exhibited at least two different activities, glucoamylase and α-amylase, and the former was found to be the major one (70%) on treatment of the crude enzyme fraction at pH 3.5 and 45°C. Glucoamylase, which was purified to homogeneity as judged by disc-gel electrophoresis, showed considerable thermostability and resistance to heavy metal ions. The purified enzyme rapidly degraded rabbit liver glycogen and potato amylopectin to the limits of 98% and 81%, respectively, which were identical to those with the enzymes of Aspergillus niger and Rhizopus delemar. The Km values of glucoamylase of K-27 for oligosaccharides were almost the same as those of A. niger and about half those of R. delemar, and the values for polysaccharides were about half those of GIII of R. delemar and 1/300-1/2700 of those of the enzyme of A. niger. The Vmax values for all the substrates tested resembled those of the enzyme of R. delemar GIII and were 1.5-2 times as high as those of the enzyme of A. niger (Ref. 8).
The glucoamylase of K-27 showed higher digestibility of raw starch than the enzymes of A. niger and R. delemar. The α-amylase alone showed little raw starch digesting activity but it stimulated the activity of the glucoamylase greatly.
