SPECIFICITY OF THE HUMAN INTESTINAL DISACCHARIDASES AND IMPLICATIONS FOR HEREDITARY DISACCHARIDE INTOLERANCE*

Abstract

Human intestinal mucosa homogentaes hydrolize a number of different disaccharides. Heat inactivation of the homogenates at varying temperatures in 0.01 M sodium phosphate buffer, pH 7.0, has indicated that these disaccharidases activities are accounted for by a mixture of at least six separate enzymes-namely, five different *= 224 -glucosidases, four of which have maltase activity, and lactase, which hydrolys=zes both *= 225 -glucosides and *= 225 -galactosides. The *= 224 -glucosidases separated are:maltase Ia (=isomaltase), maltase Ib (=invertase), maltase II, maltase III, and trehalase. Hereditary deficiency of single intestinal disaccharidases is known to appear in children. From the specificity of human intestinal disaccharidases, it may be expected that intolerance for isomaltose, sucrose, or trehalose can appear as an isolated defect. Lactose intolerance will probably allways be associated with cellobiose intolerance; and maltose intolerance, which demands the simultaneous absence of four separate enzymes, will probably allways be acompanied by intolerance for sucrose and isomaltose. As far as the disaccharidase-deficient patients described in the literature have been examined, their defects accord with this theory