Properties and human origin of two angiotensin-I-converting enzyme inhibitory peptides isolated from a tryptic hydrolysate of human serum albumin

Two angiotensin-I-converting enzyme (ACE) inhibitory peptides were isolated from a tryptic hydrolysate of human serum albumin (HSA), The peptides were identified by sequencing and other analyses as Ala-Trp and the nonapeptide Ala-Phe-Lys-Ala-Trp-Ala-Val-Ala-Arg (human albutensin A), corresponding to f(213-214) and f(210-218) of HSA, respectively, Synthetic versions of both peptides had previously been shown to have ACE inhibitory activity. The pr esent results are the first to show that these peptides have a potential na tural origin in humans. Additional studies were done to define the inhibito ry properties of these peptides, as they had not been previously reported, The dipeptide and nonapeptide showed dose-dependent inhibition of ACE, with IC50 values of 12 and 1.7 mu mol/l, respectively. Lineweaver-Burk plots su ggested that Aia-Trp is a competitive inhibitor, and that human albutensin A is a noncompetitive inhibitor.