Extracellular sucrose is hydrolyzed to yield glucose and fructose in a reaction catalyzed by the sucrase domain of sucrase-isomaltase (Conklin et al. 1975). In the body, this enzyme is found on the external face of enterocytes in microvilli of the small intestine (Hauri et al. 1985). The sucrase-isomaltase polypeptide is cleaved into its sucrase and isomaltase domains, which remain associated and, by analogy to the corresponding pig enzyme, are thought to dimerize (Cowell et al. 1986).