Comparison of a salivary 14 kD protein displaying cysteine proteinase inhibitory activity with other salivary cystatins.

An acidic protein with a molecular weight of 14 kD and a cysteine proteinase inhibitory activity was isolated from human whole salive. It was classified therefore as a cystatin. Fractionation of whole saliva by FPLC ion-exchange chromatography, followed by immunochemical analysis with monoclonal antibodies, indicated that this protein, designated 14 kD/E8B, eluted in a single peak, which comprised 6% of the total salivary cystatin-activity. The 14 kD/E8B cystatin had nearby 5 times less apparent affinity for papain than chicken egg cystatin. In addition to 14 kD/E8B cystatin, four other cystatins were separated, having pI values of 4.5 and 4.7. One of these appeared together with amylase. Furthermore a protein having a pI of 6.7 was isolated, which accounted for approximately 50% of the total cystatin activity present in whole saliva. The total cystatin activity in unstimulated whole saliva showed at least a three fold difference between individuals. Specific cystatin activity, based on protein content, was highest in saliva derived from the submandibular gland. In addition, cystatin activity could be detected in sublingual and labial saliva, whereas parotid saliva displayed little activity and palatinal saliva no activity at all.