Sucrase

Sucrase is a digestive enzyme that catalyzes the hydrolysis of sucrose into glucose and fructose. In humans and many mammals, the principal intestinal sucrase activity comes from the brush-border enzyme complex sucrase–isomaltase (SI), located on the microvilli of enterocytes in the small intestine.

Structure and mechanism: The SI polypeptide is proteolytically processed into two catalytic subunits; the sucrase subunit provides the ability to cleave sucrose, while isomaltase handles certain α-1,6-linked glucans. The sucrase reaction is sucrose plus water yielding glucose and fructose. This activity is essential for efficient digestion of dietary sugars; some organisms have separate invertases or sucrases that may be secreted or cell-surface associated.

Physiology: In humans, sucrase activity increases after weaning and is essential for digestion of dietary sucrose. The enzyme functions in the small intestine at the brush border, contributing to postprandial glucose and fructose availability.

Clinical relevance: Congenital sucrase–isomaltase deficiency (CSID) is a genetic disorder characterized by impaired digestion of sucrose and certain starch-derived carbohydrates; symptoms include chronic diarrhea, abdominal pain, and growth delay. Diagnosis can involve enzymatic assays, breath tests, or genetic testing. Management includes restricting sucrose and starch and, when needed, enzyme replacement with sacrosidase.

Other organisms: In yeast, fungi, and bacteria, invertases or sucrases perform similar hydrolysis of sucrose and contribute to carbon metabolism and fermentation.