Abstract
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 pre-pared 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 isomalt-ase 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.
