Comparative study of the action of bovine duodenal proteinases (duodenases) on polypeptide substrates

A comparative study of substrate specificity of bovine duodenal proteinases--chymotrypsin-like duodenase (ChlD) and dual-specificity duodenase (dsD)--was carried out using oligopeptide substrates (human proinsulin, glucagon, melittin, angiotensinogen fragment 1-14). ChlD displayed mainly chymotrypsin-like properties towards these substrates, hydrolyzing peptide bonds carboxy-terminally to bulky aliphatic or aromatic residues. In melittin, ChlD additionally cleaved peptide bonds after Thr and Ser residues. Dual-specificity duodenase (dsD) significantly restricted its specificity to only trypsin-like or only chymotrypsin-like or displayed full activity, combining both specificities, depending on substrate. Both ChlD and dsD efficiently hydrolyzed a single peptide bond (Phe8--His9) in angiotensinogen fragment 1-14. The kinetic parameters of angiotensinogen fragment 1-14 cleavage by ChlD and dsD were determined (k(cat)/K(m) = 80,500 M(-1) x sec(-1) for ChlD and 103,000 M(-1) x sec(-1) for dsD).