Protein Synthesis Controls the Activity of Maltase‐Glucoamylase and Sucrase‐Isomaltase in non‐intestinal Tissues

Abstract

Maltase‐Glucoamylase (MGAM) and Sucrase‐Isomaltase (SI) are α‐glucosidases of the membrane of small intestinal enterocytes responsible for the digestion of dietary carbohydrates into glucose and other monosaccharides. MGAM and SI mRNA expression, protein synthesis and catalytic activity of MGAM and SI are found predominantly in enterocytes; however, they are also found in lower amounts in other non‐intestinal tissues, notably blood leukocytes and kidney cells. Little information exists on the functions, the mRNA expression, the nature of the respective proteins and catalytic properties of MGAM and SI in non‐intestinal tissues. To correlate the transcription, synthesis and activity of these enzymes, we measured the mRNA expression of MGAM and SI; the catalytic activities of maltase, sucrase, and isomaltase; and the presence of the respective proteins in small intestine and other tissues such as spleen, kidney and pancreas of 8 weeks old mice. Small intestine showed the highest level of mRNA expression of MGAM and SI, as well as their typical WB pattern and catalytic activity. Blood, kidney, and spleen displayed substantial amount of mRNA expression particularly for MGAM, but lower than small intestine. The variable proportions of maltase/sucrase and sucrase/isomaltase enzyme activities and the WB protein bands, indicated differences in the protein synthesis and processing among different tissues. We conclude that mRNA expression and the corresponding protein translation control the activities of MGAM and SI among tissues.