The sedimentation properties of the intestinal alpha-glucosidases of normal human subjects and of patients with sucrose intolerance.

Abstract

The maltase‐isomaltase, maltase‐sucrase and glucoamylase of the human intestinal mucosa have been solubilized by Triton X‐100 and submitted to centrifugation in a mannitol gradient. Under these conditions, the three enzymes sediment together in a 10 S fraction; with one normal mucosa out of 10 which were investigated a supplementary 13 S peak of both glucoamylase and maltase‐isomaltase was observed.Several experimental conditions, like treatment of the extracts at 45° or solubilization of the α‐glucosidases by papain in the absence of potassium ions, induced an important inactivation of the maltase‐isomaltase and deep alterations in the sedimentation profile of the 3 glucosidases: the glucoamylase and the residual maltase‐isomaltase were distributed in 3 fractions with 13 S, 10 S and 6–7 S sedimentation coefficient, whereas the maltase‐sucrase was mostly present as a 7 S structure. In sucrose intolerance, the maltase‐sucrase is absent and the activities of the maltase‐isomaltase and glucoamylase are significantly reduced. The residual enzymes were ‐recovered as 13 S and 6 S structures instead of the normal 10 S species.These observations allow the conclusion that the three α‐glucosidases are naturally linked to each other in the normal mucosa and that the alteration of one of them induces a structural rearrangement of the 3 enzymes. The absence of maltase‐sucrase in patients with congenital intolerance to sucrose can be regarded as the result of a single mutation of the corresponding structural gene and as the cause of a reorganization of the two other α‐glucosidases; this reorganization can explain a partial loss of the enzymatic activity.