The purification and partial characterization of human salivary kallikrein

Abstract

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 p I of 4.0 and an M r of 27000 as determined by dodecyl sulfate gel electrophoresis. On the other hand, sedimentation equilibrium data and the amino acid composition give an M r value of only 9600. The enzyme could be a rather asymmetric molecule. The circular dichroism spectrum shows a minimum at 200 nm with [ θ] = −28000 deg · cm 2 · dmol −1. The spectrum suggests that the enzyme structure contains polyproline form II helix together with β-turns. This structure is stable in the presence of dodecyl sulfate.