The basic proline-rich proteins in human parotid saliva from a single subject.

Eleven Chromatographic fractions of basic proline-rich proteins isolated from parotid saliva from a single donor showed similar but not identical chemical compositions; proline, glycine and glutamic acid-glutamine accounted for 70–80 per cent of the total residues in the proteins. The basic amino acids, lysine and arginine, accounted for a further 10 per cent. All the proteins were in freshly-collected saliva and did not result from post-secretory proteolysis. The most basic of the proline-rich proteins, I-B9, was purified and characterized. The amino terminal residue was serine and the carboxyl terminal residue arginine. The molecular weight determined by quantitative end-group analyses was 9000–9500. Protein I-B9 was resistant to hydrolysis by collagenase and Staphylococcus aureus protease, whereas papain and subtilisin extensively degraded it. I-B9 fragments from clostripain and elastase digestions were isolated for use in sequence determination. Basic proline-rich proteins, acidic proline-rich proteins and proline-rich glycoprotein accounted for 23, 30 and 17 per cent, respectively of the total protein in the parotid saliva.