title: The proteins of the content of the secretory granules of the rat parotid gland.
abstract: The proteins of the secretory granules of the rat parotid gland were characterized by sodium dodecylsulfate gel electrophoresis, by chromatography of [3-H]proline-labeled proteins on DEAE-cellulose and by amino acid analysis. Sodium dodecylsulfate gel electrophoresis of the secretory granule content showed five principal proteins and a limited number of minor components. Only two of the principal bands could be identified as known secretory enzymes of the parotid gland. One was identified as the alpha-amylase and one as deoxyribonuclease. Peroxidase and ribonuclease form minor portions of the secretory proteins. The other three major proteins constitute, together, about 60% by weight, of the secretory granule content proteins. Of these, one which represents more than 30% of the total granule protein was found to contain uniquely high amounts of leucine residues (21 mole%). Another one of these principal proteins was relatively rich in cysteine residues (7 mole%). The fifth principal protein was found to contain high amounts of proline (28 mole%) glutamic acid (17 mole%) and glycine (18 mole%) residues. Its amino acid composition was very similar to that of the proline-se granules. This protein, however, differed from the "membranous" proline-rich proteins by several criteria. Two minor glycoproteins of the secretory granule content were also found to be rich in proline residues (37 mole%). As with the other proline-rich proteins of the granule, they contained no sulphur-containing amino acids, stained faintly pink with Coomassie Blue and were underestimated by the Lowry method. They differ however, from all the other proline-rich proteins of the granule by having a significantly higher content of threonine, less glycine (9 mole%) and much less glutamic acid (3 mole%). Of the principal proteins, only the deoxyribonuclease and the half-cystine-rich proteins were positively stained by periodic acid Schiff staining. The possible functions of the leucine-rich, the half cystine-rich and the various proline-rich proteins are discussed.
mesh_terms: D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002848:Chromatography, DEAE-Cellulose; D003594:Cytoplasmic Granules / Q000032:analysis / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D006801:Humans; D008970:Molecular Weight; D010306:Parotid Gland / Q000032:analysis / Q000378:metabolism*; D011392:Proline / Q000378:metabolism; D011506:Proteins / Q000032:analysis*; D051381:Rats; D013045:Species Specificity
chemical_list: D000596:Amino Acids; D011506:Proteins; D011392:Proline