Action Mechanisms of B. macerans Enzyme and Preparation of Cyclodextrins

Abstract

B. macerans enzyme has been known by the name of BMA or cyclodextrin glycosyltransferase which has three different actions on α-1, 4-glucan. These actions are cyclization, coupling and disproportionation. As these actions occur simultaneously, a fewer study of the mechanism of macerans enzyme actions has been done. 1) The author has studied on the action of macerans enzyme using various maltooligosaccharides and cyclodextrins (CDs) in order to prepare various CDs selectively, and tried to clarify some action mechanisms and action pattern . Cyclization proceeded as exo-type attack from non-reducing end of oligosaccharides, α-CD was easily transfered to G1-G4 to form G7, G8, ---by coupling reaction at the initial stage of the reaction. G2 was the most effective acceptor in the maltodextrins we examined. The rate of coupling reaction of β-CD was extremely slower than α-CD . Disproportionation which is the transferation between maltooligosaccharides showed a certain pattern in which primarily Gn-2 moiety was transfered to another Gnmolecule to form G2n-2 and G2. From the experiments of the effects of complexing agents, we observed that the addition of SDS induced strongly the formation of α-CD from maltodextrin and other hand, β-CD was produced by the existence of Triton X-100. Stubbed CD which connected glucosyl, maltosyl---by α-1, 6 linkage with CD was also formed by the addition of complexing agents such as SDS to branched substrates . From the above results, the author infered that the action pattern of macerans enzyme may be changed by the conformational change of substrate . 2) The author proposed a scheme of α, β-CD formation. Accumulation of β-CD by the prolonged period of the reaction was elucidated by the scheme. 3) A new method of CD preparation was proposed . The principle of the method is that unreacted linear and branched dextrin in the macerans enzyme digest of starch are hydrolyzed to glucose by incubation with glucoamylase. CDs were fractionated by precipitation by addition of organic solvents such as acetone .