Fine Structure of Secretory Granules in Mammalian Submaxillary Glands

Abstract

In exocrine glands macromolecules synthesized for secretion are mainly segregated and sequestered in specific organelles within cells. It is now established that the serine protease kallikrein, and the digestive enzyme amylase, are stored intracellularly in membrane-bounded organelles. Trypsin-like enzymes isolated from the rat submaxillary gland are probably similarly stored in granules. It is evident from this study and those of Shackleford and coworkers (see Shackleford & Wilborn, 1968) that mammalian sub-maxillary glands show marked differences in the morphology of the various acinar and duct cells and the granules which contain secretory enzymes and other macromolecules. The question therefore arises as to which granules within which cells contain kallikrein, trypsin-like enzymes and amylase. The precise cellular location of the granules which contain the secretory enzymes may provide some insight into the possible physiological role of submaxillary kallikrein and the trypsin-like proteases.