Determination of the Amino Acid Sequence of Porcine Trypsin by Sequenator Analysis

Abstract

The amino acid sequence of porcine trypsin has been determined by sequenator analysis of the reduced and S-pyridylethylated protein and of eight suitably chosen peptide fragments. The fragments were the products of cleavage by autolysis, cyanogen bromide, 2-(2-nitrophenylsulfenyl)-3-methyl-3-bromoindolenine, hydroxylamine, and trypsin, respectively. All but the last 2 of the 223 amino residues were uniquely placed by these analyses. Comparison of this sequence with that of bovine trypsin indicated 82% identity, corresponding to a unit evolutionary period of approximately 3 million years. Of the 41 amino acid substitutions, 36 are on the surface of the bovine enzyme and 5 in the interior. The latter are of the conservative type. All residues known to be components of the active site of bovine trypsin are present in identical positions in porcine trypsin, but the porcine enzyme does not possess the calcium binding site identified in the bovine enzyme. © 1973, American Chemical Society. All rights reserved.