New protein inhibitors of cysteine proteinases in human saliva and salivary glands.

New protein inhibitors of cysteine proteinases were found in human saliva and salivary glands. The inhibitory potency present in saliva against ficin is about 30% of that in serum: 1 ml of saliva gives 100% inhibition of 1 nmol of ficin. The same amount of saliva causes no inhibition of 1 nmol of trypsin. The salivary inhibitors occur as multiple forms with different isoelectric points (pI of 4.5-4.7, 5.8, 6.8, 7.8 and 8.2) and different molecular masses of approximately 16, 11, 10, 9.5 and 9 kDa. The inhibitor forms having molecular masses of less than 11 kDa have not yet been described by other authors. The salivary inhibitors have a high thermal stability and a high stability both in alkaline and acidic solutions.