N-Terminal amino acid sequence of rat tonin: homology with serine proteases

Abstract

The amino-terminal sequence of rat submaxillary gland tonin, an endopeptidase responsible for the conversion of angiotensinogen, the tetradecapeptide renin substrate, or angiotensin I to angiotensin II is presented. Isoleucine and proline occupy the amino- and carboxy-terminal residues, respectively. The N-terminal sequence analysis permitted the identification of 34 out of the first 40 residues of the single polypeptide chain composed of 272 amino acids. These results showed an extensive homology with the sequence of many serine proteases of the trypsin-chymotrypsin family. This information, coupled with the slow inhibition of tonin by DFP, classified this enzyme as a selective endopeptidase of the active serine protease family.