AJP - Gastrointestinal and Liver Physiology, Vol 265, Issue 6 1141-G1149, Copyright © 1993 by American Physiological Society
Murine intestinal disaccharidases: identification of structural variants of sucrase-isomaltase complex
R. Quezada-Calvillo, A. J. Markowitz, P. G. Traber and B. J. Underdown
Department of Pathology, McMaster University, Hamilton, Ontario, Canada.
This study was directed to determine the extent of variability in structure
or expression of intestinal disaccharidase [gamma-glucoamylase (gamma-GA),
sucrase-isomaltase (SI), and lactase] between different strains 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 levels of sucrase activity
(approximately 50 U/g of protein). Decreased levels of sucrase in CBA/Ca
mice were not associated with decreased levels of activity associated with
the isomaltase subunit or with decreased levels of SI mRNA expression.
High-performance liquid chromatographic gel filtration, heat inactivation,
and kinetic analysis indicated that the differences between strains in
sucrase activity might be attributed to structural differences in the
sucrase subunit of the SI complex, 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 for a greater proportion of maltase activity
(approximately 70%) than that 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 (approximately 300 U/g).
