The proline-, glycine-, glutamic acid-rich pink-violet staining proteins in human parotid saliva are phosphoproteins.

The major proteins in human parotid saliva, isolated in Fractions II-V following chromatography on Sephacryl S-200, DEAE-Sephadex A-50, or CM cellulose, contain 6 moles of phosphate per mole of protein, the phosphate probably bound to the protein via an ester linkage. This phosphate represents greater than 90% of the protein-bound phosphate in human parotid saliva. Neither purified gustin nor amylase, the two other major proteins in human parotid saliva, contain phosphate.