Val-tyr, an Angiotensin I Converting Enzyme Inhibitor from Sardines that have Resistance to Gastrointestinal Proteases

The NH₂-terminal residue of a dipeptide is an important determinant of the resistance to peptidases of porcine small mucosa. NH₂-terminal Val or Ile, and COOH-terminal Trp or Tyr dipeptides had higher angiotensin I converting enzyme(ACE)inhibitory activity and digestive resistance than other dipeptides. We defined Val-Tyr as a main inhibitor in alkaline protease hydrolyzates from sardines. Attempts to isolate and measurement of Val-Tyr were done from the short chain peptides that reduced blood pressure. The content of Val-Tyr was 51 mg per 100 g of the short chain peptides, represented 1.3% of the total ACE inhibitory activity of the short chain peptides. Isolated Val-Tyr was resistant to gastrointestinal proteases. The primary structures of fragments formed from Arg-Val-Tyr by digestive proteases were considerably different, and it was confirmed that the main peptide, Val-Tyr, was formed by intestinal proteases after digestion. The content of Val-Tyr formed from the short chain peptides by intestinal proteases after digestion was less than 10 percent of the original.