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 present results are the first to show that these peptides have a potential natural origin in humans. Additional studies were done to define the inhibitory 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 micromol/l, respectively. Lineweaver-Burk plots suggested that Ala-Trp is a competitive inhibitor, and that human albutensin A is a noncompetitive inhibitor.