The occurrence of inactive amylase within the pancreatic cell and its significance

Abstract

1. 1. The apparent amylase content of homogenates of pigeon pancreas was increased by disintegration with ballotini beads. Most of this additional amylase was released from the microsome fraction sedimenting at 18,000 g from 0.25 M sucrose. Very little was obtained from the ultramicrosome fraction subsequently spun down at 105,000 g. 2. 2. On electron microscopy, the microsome fraction was found to contain numerous vesicles which are presumed to originate from the endoplasmic reticulum. When this microsome fraction was stored in water, the inactive amylase became active and this coincided with the disappearance of vesicles from the preparation. It was concluded that the inactive enzyme was present in the interior of the vesicles and was thus rendered inaccessible to the substrate. When the enzyme was activated by rupture of the vesicles in water, it remained attached to the debris. It is therefore likely that the amylase is attached to the interior of the intact vesicle. 3. 3. Uptake of 14C-glycine by the microsome fraction is high, and especially so by the proteins not associated with ribonucleic acid, that is, the proteins of the vesicle wall. It is thus possible that the site of amylase attachment to the vesicle wall is also its site of formation.