Figure 4.

Comparison of sleeve and homogenate sucrase assays. Sucrase activity of a homogenate of a 2-cm length of mid-intestine was compared with activities measured from sleeves of the two adjacent pieces of intestine of the same mouse. All incubations were at 37°C and 50 mM sucrose, and solution conditions were always pH 7.4 Ringer’s solution with 20 mM Hepes for the sleeves, but solution conditions for the homogenates varied: either the same condition as for the sleeves (pH 7.4 Ringer’s solution with 20 mM Hepes), or else 0.1 M Na⁺ maleate at pH 7.0, pH 7.0 Ringer’s solution with 20 mM Hepes, or 0.1 M Na⁺ maleate at pH 6.0 (see symbols on figure). Ordinate values are mean values of ratios of homogenate activities to pH 7.4 Ringer’s solution/20 mM Hepes sleeve activity in the same individual mouse, with error bars denoting the SEM. (n = 4 mice). Note that sleeves and homogenates yield identical sucrase activities under identical solution conditions (ratio near 1.0 for homogenates in pH 7.4 Hepes); and that the classical Dahlqvist assay in homogenates (pH 6.0 maleate) yields a ratio of 2.0 (i.e., activities double our sleeve values measured in pH 7.4 Ringer’s solution), because sucrase activity increases considerably with decreasing pH (compare pH 6.0 and 7.0 maleate, or pH 7.0 and 7.4 Hepes) and despite the somewhat lower sucrase activity in maleate than in Hepes at the same pH (compare pH 7.0 maleate and pH 7.0 Hepes).