Abstract
Cyclodextrin glucanotransferase (CGTase) produced cyclodextrin from the nonreducing terminals of substrate starch molecule, and this would provide a clue for the classification of CGTase into an exotype of enzyme. However, random cyclization reaction was recently demonstrated by an analysis of the initial action of CGTase. Further evidence for the random attack of CGTase on soluble starch was obtained by the following experiments. In a comparison of the cleavage pattern of CGTase on the fluorescent-labeled soluble starch with Taka-amylase A (endo-type) and glucoamylase (exo-type), the characteristics of CGTase were much closer to an endo-type action than to an exo-type action; namely, a rapid decrease in the substrate molecular weight was observed. A very low production of reducing sugar, in spite of a large decrease in blue value, was another characteristic obtained for the CGTase reaction, which would suggest that the production of oligomer fragments having a reducing end group was much less than that of cyclized fragments. These results show that CGTase attacked the starch substrate not only at sites close to the nonreducing terminals in an exo-type of cleavage, but also at sites in the middle of the substrate molecule in cleavage much like an endo-type.
