Properties of proline-rich proteins from parotid glands of isoproterenol-treated rats.

This report describes the physical and chemical properties of a series of proline-rich proteins isolated from parotid glands of isoproterenol-treated rats. As described previously (Muenzer, J., Bildstein, C., Gleason, M., and Carlson, D. M. (1979) J. Biol. Chem. 254, 56235628), a dramatic increase in these proteins occurs concomitantly with hyperplasia and hypertrophy of parotid glands of rats treated with isoproterenol. These proteins, labeled in uiuo with [3H]proline, account for greater than 50% of the total soluble protein in gland homogenates and greater than 99% of the tritium incorporated was isolated as r3H]proline. Six basic proline-rich proteins (p1 values > 10) are unusually high in proline (40 to 44%), glutamine plus glutamic acid (22 to 25%), and glycine (18 to 20%) and contain varying amounts of arginine plus lysine (7 to 9%). Tyrosine, phenylalanine, cysteine, methionine, hydroxyproline, and hydroxylysine are absent, or less than 1 residue/ mol of protein. Similarily, glucosamine and galactosamine were present at less than 1 mol/mol. Fatty acids, phosphorus, calcium, and magnesium were not detected. Treatment with purified prolylhydroxylase resulted in undetectable (less than 0.1%) conversion of proline into hydroxyproline. The molecular weights of these basic proteins ranged from 15,000 to 18,000. A high apparent molecular weight (>70,000) was observed following chromatography on Sephadex G-100, but this resulted from an unusually high axial ratio of over 25. szo,,,, values range from 1.1 to 1.4. Circular dichroism spectra, characterized by a single trough at about 200 nm with ellipticities of 17 to 22 x lo3 deg cm2/dmol, suggest an unordered, random conformation. Trypsin treatment and chromatography of the resulting peptides gave a peptide with ratios of proline to glutamic acid(glutamine) to glycine of 2:l:l. Similar proline-rich proteins are present in submandibular glands of isoproterenol-treated rats and in parotid glands of normal rats.