The purification and partial characterization of human salivary kallikrein

The major arginine esterase activity in human saliva has been purified. This enzyme lowers the blood pressure of a rabbit and produces kinins in acid treated dog plasma. It is therefore a kallikrein. The kallikrein has an unusual amino acid composition: aspartic acid and glutamic acid comprise 40% of the residues; the total number of basic residues is less than 5%; glycine and proline together make up more than 40% of the residues. The enzyme has a pI of 4.0 and an Mr of 27 000 as determined by dodecyl sulfate gel electrophoresis. On the other hand, sedimentation equilibrium data and the amino acid composition give an Mr value of only 9600. The enzyme could be a rather asymmetric molecule. The circular dichroism spectrum shows a minimum at 200 nm with [theta] = - 28 000 deg X cm2 X dmol-1. The spectrum suggests that the enzyme structure contains polyproline form II helix together with beta-turns. This structure is stable in the presence of dodecyl sulfate.