Characterization of Mucosal Disaccharidases from Human Intestine

Abstract

In this study, we used a brush border membrane (BBM) preparation from human small intestine to analyze the proportion and the activity of major intestinal disaccharidases, including sucrase-isomaltase (SI), maltase-glucoamylase (MGAM) and lactase-phlorizin hydrolase (LPH). SI, MGAM and LPH respectively constituted 8.2%, 2.7% and 1.4% of total BBM protein. The activity of SI and LPH decreased threefold after purification from the brush border membrane, which highlights the effect of membrane microdomains on the functional capacity of these enzymes. All of the disaccharidases showed optimal activity at pH 6, over 50% residual activity between pH 5 to pH 7, and increasing activity with rising temperatures up to 45 °C, along with a stable functional structure. Therefore the enzymes can withstand mild intraluminal pH alterations with adequate function, and are able to increase their activity with elevated core body temperature. Our data provide a functional measure for characterization of intestinal disaccharidases under different physiological and pathological conditions.

Keywords: enzyme activity; intestinal disaccharidases; pH profile; thermal activity profile.

Figure 1

The effect of pH and temperature on the disaccharidase activities from human intestinal brush border membrane preparation. (A) The pH profile for sucrase, maltase and lactase activities was determined by measuring the enzyme activities in phosphate citrate buffer with different pH values ranging from 3 to 8; (B) The enzyme reactions were performed at different temperatures from 25 °C to 80 °C in phosphate citrate buffer at pH 6 to determine the thermal activity profile; (C) The enzyme samples in phosphate citrate buffer pH 6 were treated at the indicated temperature for 1 h and then used to measure the residual activity at 37 °C. Error bars: standard deviation.