The amino-acid residues on the C-terminal side of the cleavage site of angiotensinogen influence the species specificity of reaction with renin

The N-terminal sequences of human and canine Angiotensinogen and two hybrid sequences were synthesized and used to determine whether the species specificity of Renin is influenced by amino-acid residues adjacent to the cleavage site. kcat/Km for the generation of angiotensin I from the N-terminal tridecapeptide of human Angiotensinogen by canine Renin is 0.37% of that observed when the N-terminal tetradecapeptide from canine Angiotensinogen is used as a substrate. Replacement of the valine residue at P'1 in the human tridecapeptide with the leucine residue from the canine sequence triples kcat and improves Km 4-fold. Replacement of isoleucine residue at P'2 with the valine residue from the canine sequence enhances Km 8-fold. Substitution of the histidine residue at P'3 with the tyrosine serine sequence of canine Angiotensinogen increases kcat an order of magnitude. Results obtained with the synthetic substrate are similar to those observed with the protein substrates. Canine Renin does not cleave human Angiotensinogen. Also, kcat/Km of canine Renin for its homologous substrate is about 6-times greater than the kcat/Km value for human Renin acting on human Angiotensinogen.