Critical Reviews in Oral Biology and Medicine, 4(3/4):517-524 (1993) The Bi-Immunoreactive Proteins of the Perinatal Submandibular Gland: Similarity to the Major Parotid Gland Protein, RPSP

ABSTRACT: The BI-immunoreactive proteins of type Im cells of the perinatal rat submandibular gland are immunologically cross-reactive with proteins of both the sublingual and parotid glands; in particular, protein SMG-A appears similar to a major parotid protein. We isolated SMG-A and the parotid protein (known as Ml or leucine-rich protein), prepared polyclonal antibodies to them, and compared their biochemical properties and immunological reactivities. They were identical in their molecular weight on SDS-PAGE (23.5 kDa), tenacious binding to Affi-gel Blue, isoelectric point (pH 4.53), and proteolysis to a 14 kDa peptide: Antibodies to SMG-A showed reactivity with protein SMG-C, a product of the neonatal type I cells, as well as with proteins SMG-BI and SMG-B2, contrasted with the absence of reactivity of anti-Ml IgG with these proteins. Anti-MI reacted with the "parotid secretory protein " (PSP) of the mouse, and MI appears to be the homologue, in the rat, of mouse PSP. KEY WORDS: rat and mouse salivary glands, perinatal and adult secretory proteins, protein purification, expression during development