馬鈴しょでんぷん粒の酵素分解

Abstract

Bacillus circulars F-2 can digest potato starch granules added to the medium as a sole carbon source. Scanning electron microscopic observation of potato starch granules recovered from cultured medium revealed that the granules were degraded gradually from their surface resulting in elongated granules with layered structure on their surface. The bacterium produces extracellular amylase when potato starch granules are used as a carbon source. Soluble starch or maltose, used as a carbon source instead of potato starch granules, induced little amylase. The amylase was purified from the culture supernatant to show a single protein band on SDS polyacrylamide gel electrophoresis and its general properties were studied. When acted on soluble starch, the purified enzyme produced maltohexaose alone in the early stage of hydrolysis. On further incubation, maltotetraose and maltose were produced with concomitant decrease of maltohexaose. The enzyme seems to act on amylaceous polysaccharides exowisely, by liberating maltohexaose successively from their nonreducing ends. Although the enzyme showed almost the same digestive activity as porcine pancreatic a-amylase and Streptococcus bovis α-amylase toward corn starch granules, it exhibited far higher digestive activity than those amylases toward potato starch granules.