DUODENASE, A NEW SERINE-PROTEASE OF UNUSUAL SPECIFICITY FROM BOVINE DUODENAL MUCOSA - PRIMARY STRUCTURE OF THE ENZYME

The complete amino acid sequence of duodenase, a new serine endopeptid ase from bovine duodenal mucosa, has been determined. The sequence was reconstructed by the automated sequence analysis of the peptides obta ined after cleavage with trypsin, Staphylococcus aureus V8 protease, c yanogen bromide and duodenase. The enzyme is composed of 226 amino aci d residues yielding a molecular mass of 29.06 kDa. The presence of six cysteine residues and one potential sugar-chain-binding site at Asn50 was revealed. A predicted catalytic triade characteristic of the seri ne proteases was traced in the duodenase primary structure at the corr esponding positions (His44, Asp87 and Ser181 in the sequence). Compari son of the sequence of duodenase with the other known primary structur es of mammalian serine proteinases reveales the duodenase identity to granzymes from human and mice, human cathepsin G and mast cell chymase s from rat, and gives an overall sequence identity of 47-55% with the mentioned enzymes. Alignment of the known serine protease and duodenas e primary structures showed unique amino acid residues within the duod enase substrate-binding pocket at positions 189 (Asn) and 226 (Asp) (t he bovine chymotrypsinogen A numbering). These results are discussed w ith respect to the relation between the duodenase unique residues with in the primary specificity pocket S-1 and the unusual dual specificity of the enzyme.