In children with CSID, starch digestion correlates well with measures of sucrase activity.

Major conclusions: The sucrase and isomaltase domains are closely interacting in the mature protein.

The activity of aminopeptidase and sucrase-isomaltase in the test animals was also significantly lower than in the controls.

Clinical studies suggest that starch may be poorly digested in those with congenital sucrase-isomaltase deficiency (CSID).

Small intestinal breakdown of starch-derived substrates occurs through the mechanisms of small intestinal brush border enzymes, maltase-glucoamylase and sucrase-isomaltase.

Control subjects consisted of healthy family members and a group of children with functional abdominal pain with biopsy-proven sucrase sufficiency.

General significance: There has been little experimental evidence previously of the effects on activity of interactions between the sucrase-isomaltase enzyme domains.

Sterol absorption in intact enterocytes parallels the absorption measured in BBMV, provided that both model systems are normalized to equal sucrase activity.

For example, the enzyme that breaks down sucrose (table sugar) is called sucrase; cellulose (plant starch) is broken down by cellulase.

Mutational analysis provided evidence that these residues in isomaltase can also affect activity in the partner sucrase domain, suggesting a close interaction between the domains.

Sucrase deficiency was previously documented in study subjects by both duodenal biopsy enzyme assays and C-sucrose BT.