Rat intestinal microvillus membrane sucrase-isomaltase is a single high molecular weight protein and fully active enzyme in the absence of luminal factors.

Sucrase-isomaltase immunoprecipitated from brush border of an intestinal transplant lacking pancreatic proteases was found to be a single, high molecular weight protein. Elastase digestion converted this protein into two subunits which co-migrated on electrophoresis with those normally found on the microvillus membrane. The high molecular weight form had full sucrase and isomaltase activities.