Some characteristics of early appearing isomaltase in intestinal mucosa of suckling rat.

Characteristics of early appearing free isomaltase in the soluble fraction were investigated in rat intestinal mucosa. Soluble isomaltase and membrane-bound sucrase-isomaltase complex were prepared from 15-day-old rat intestine. Immunochemical properties, optimal pH and heat sensitivity of soluble isomaltase were compared with those of membrane-bound isomaltase. Optimal pH of free isomaltase in the soluble fraction was lower than that of membrane-bound isomaltase. Soluble and membrane-bound isomaltase showed different sensitivities for temperature. Furthermore, membrane-bound isomaltase in 15-day-old suckling rat intestine gave a single line with antiserum. However, soluble isomaltase gave no precipitin line. From these results, it could be concluded that soluble isomaltase is not derived from the isomaltase moiety of membrane-bound sucrase-isomaltase complex as a result of mechanical fragility and rather it would be lysosomal in origin.