MURINE INTESTINAL DISACCHARIDASES - IDENTIFICATION OF STRUCTURAL VARIANTS OF SUCRASE-ISOMALTASE COMPLEX

This study was directed to determine the extent of variability in stru cture or expression of intestinal disaccharidases [gamma-glucoamylase (gamma-GA), sucrase-isomaltase (SI), and lactase] between different st rains of mice. Reduced levels of sucrase activity (approximately 20 U/ g of protein) were observed in three strains of mice belonging to the CBA/Ca lineage. Four other strains of mice analyzed exhibited higher l evels of sucrase activity (approximately 50 U/g of protein). Decreased levels of sucrase in CBA/Ca mice were not associated with decreased l evels of activity associated with the isomaltase subunit or with decre ased levels of SI mRNA expression. High-performance liquid chromatogra phic gel filtration, heat inactivation, and kinetic analysis indicated that the differences between strains in sucrase activity might be att ributed to structural differences in the sucrase subunit of the SI com plex, thus rendering it more susceptible to cleavage and inactivation. However, no differences in kinetic properties of the sucrase subunit were observed between strains. Murine gamma-GA was found to account fo r a greater proportion of maltase activity (approximately 70 %) than t hat observed in other species (i.e., approximately 20%). In addition, CBA/Ca mice were found to be deficient in intestinal maltase activity (approximately 60 U/g) compared with the other strains studied (approx imately 300 U/g).