| This thesis describes the identification and characterization of two abundant products of rat submandibular gland acinar cells. Chapter 1 outlines the purification of blood group A-reactive mucin from submandibular gland extract. This glycoprotein, the characteristic product of mucous acinar cells, is approximately 103 kDa in size, and contains 64% carbohydrate by weight. Chapter II describes a novel family of submandibular gland-specific secretory proteins collectively termed the glutamic acid/glutamine-rich proteins (GRP). The GRP are major component of rat extraparotid saliva.; A cDNA library was constructed from rat submandibular gland poly(A){dollar}sp+{dollar} RNA, and clones encoding GRP isolated. Northern blot analysis of rat submandibular gland mRNA using GRP clone ID22 as a probe demonstrated the presence of two homologous GRP transcripts, approximately 950 and 1050 bases in length. In vitro translation of GRP mRNA gave rise to two primary translation products, consistent with the two mRNAs seen by northern blot analysis. The GRP purified from submandibular gland extract resolved as 4-5 immunologically related proteins by SDS-PAGE. The additional GRP species present in gland extract may arise by post translational proteolysis. A nearly full length GRP cDNA, IIIC8, was identified and sequenced. The deduced amino acid sequence of IIIC8 contained 35% Glu + Gln, and 15% Pro. Half the coding region of IIIC8 was comprised of a highly conserved 23 amino acid sequence, tandemly repeated four times with a degenerate fifth repeat.; The function of the GRP in rat saliva is not known. These proteins bear a striking architectural resemblance to the well characterized salivary proline-rich proteins (PRP). Like the acidic PRP, the GRP bind to hydroxyapatite, and may therefore function as inhibitors of calcium phosphate precipitation from saliva, or as components of enamel pellicle. |
