This is a tyrosine phosphorylated angiotensin II peptide with a substrate sequence specificity for chymase to act. This is an octapeptide hormone that is formed as a result of the action of human heart chymase, a chymotrypsin-like serine protease on the Phe-His bond of Angiotensin I. The ideal susbtrate for human heart chymase should contain this peptide sequence, and has been demonstrated that the Pro-Phe sequence in P2-P1 positions of peptide substrates is highly favored by leukocyte chymotrypsin-like proteinases such as chymases and cathepsin G.