Gastrointestinal digestion of starch. I. The action of oligo-1,6-glucosidase on branched saccharides.

Digestion of starch in mammals occurs chiefly in the mouth and small intestine through the catalytic activity of ar-amylase and maltase (a-glucosidase). Extensive cw-amylolysis of amylose and amylopectin results in the formation of maltose, glucose, and a mixture of branched oligosaccharides (cr-amylase dextrins) (1). The latter compounds, whose structure is currently being investigated by several groups (2, 3), contain the a-l,6 linkages of the amylopectin fraction intact, since these linkages are not subject to hydrolysis by a-amylase (4). Meyer and Gonon (4) have recently suggested that, ‘if hydrolysis of amylopectin by ar-amylase is carried out to completion, isomaltose is the sole branched product. Glucose is subsequently absorbed through the intestinal wall. Maltose is hydrolyzed to glucose by intestinal maltase and absorbed as glucose (5). Any maltose which escapes hydrolysis in the intestine is subsequentlyhydrolyzed by maltase present in the blood (5). We have recently shown (6) that intestinal mucosa contains a new enzyme termed oligo-1,6-glucosidase, which specifically hydrolyzes the a-l,6 linkages of isomaltose, “panose, ” and cr-amylase dextrins.’ The three enzymes, a-amylase, oligo-1 ,6glucosidase, and maltase, catalyze the essentially complete digestion of starch in the gastrointestinal tract. Oligo-1 ,6-glucosidase differs in its action from amylo-l ,6-glucosidase and R enzyme. It is the purpose of the present report to describe the activity and properties of this new enzyme.