Isomaltooligosaccharides (IMO), sweeteners derived from corn-starch, selectively promote the growth of bifidobacteria in the human intestine. The metabolic fate of IMO in healthy men was investigated. The expiration rates of excess (13)CO2 and hydrogen of six men were measured while sedentary and while taking physical exercise after the (13)C-labeled IMO intakes. The breath H2 excretion kept at a constant state after IMO ingestion in the sedentary test and increased in the exercise test. The serum glucose and serum insulin increased 30 min after IMO ingestion. The (13)CO2 recoveries were 28.7% in the sedentary test and 60.9% in the exercise test. These recoveries were 70-80% compared those of maltose. These results indicated that a part of IMO was digested and the residual IMO was fermented by intestinal flora. The energy value of IMO might be about 75% of that of maltose.
A mutant of Saccharomyces cerevisiae defective in the cell wall beta-glucan structure was obtained. The mutant cells are extremely sensitive to (beta 1-3)-glucanase digestion and mild alkali treatment. Structural analysis revealed that the alkali-insoluble, skeletal glucan from wild type cells contains two components, a (beta 1-3) linked glucan with a laminated structure, and a highly branched glucan containing predominantly (beta 1-6) linkages. The mutant cells lack the latter component.
An isomaltotriose-producing dextranase II, detected in the culture supernatant of Flavobacterium sp. M-73, was purified to an electrophoretically pure state. Successive chromatography on hydrophobic columns of Amberlite CG-50 and aminooctyl-Sepharose was very effective as the first step of purification. Further purification of the enzyme was performed by affinity column chromatography on isomaltotriose-Sepharose and preparative polyacrylamide gel electrophoresis. T he purified enzyme was shown to be a monomer and had a molecular weight of 114,000. Dextranase II was most active at pH 7.0 and 35°C. It was stable at 4°C for 24hr over a pH range of 6.5~12.0 and up to 35°C on heating for 10 min. This enzyme had a strict specificity for consecutive a-l ,6-glucosidic linkages and readily hydrolyzed clinical dextran and Sephadex gels. The degree of hydrolysis of clinical dextran was 31% expressed as apparent conversion into D-glucose. The amount of isomaltotriose in the hydrolyzate was determined to be 63%.
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