Ultrastructural localization of salivary acidic proline-rich proteins from Macaca fascicularis.

Using an indirect immunoferritin method, the subcellular distribution of acidic proline-rich proteins (MPRP) in the acinar cells of the macaque parotid and submandibular glands was defined. MPRP was found in the "spherule" substructure of the secretory granules as well as in specific Golgi transfer vesicles and in vesicles budding from the Golgi apparatus. The data suggest that the acidic proline-rich proteins of the primate Macaca fascicularis are synthesized and packaged by conventional exocrine mechanisms. In addition, these proteins appear to be packaged and transferred to the secretory granules of parotid and submandibular gland acinar cells as discrete aggregates that remain as a separate "spherule" area in the secretory granules.