Kinetics of the inhibition of renin and angiotensin I-converting enzyme by flaxseed protein hydrolysate fractions

Enzymatic hydrolysates from flaxseed protein were investigated for in vitro inhibition of angiotensin I-converting enzyme (ACE) and renin activities. Pepsin, ficin, trypsin, papain, thermolysin, pancreatin and Alcalase were used to hydrolyze flaxseed proteins followed by fractionation using ultrafiltration to isolate low-molecular-weight peptides, and separation of the Alcalase hydrolysate into cationic peptide fractions. Using N-(3-[2-furyl]acryloyl)-phenylalanylglycylglycine as substrate, the protein hydrolysates showed a concentration-dependent ACE inhibition (IC₅₀, 0.0275-0.151 mg/ml) with thermolysin hydrolysate and Alcalase cationic peptide fraction I (FI) showing the most potent activity. Flaxseed peptide fractions also showed no or moderate inhibitory activities against human recombinant renin (IC₅₀, 1.22-2.81 mg/ml). Kinetics studies showed that the thermolysin hydrolysate and FI exhibited mixed-type pattern of ACE inhibition whereas cationic peptide fraction II inhibited renin in uncompetitive fashion. These results show that the protein components of flaxseed meal possess peptide amino acid sequences that can be exploited as potential food sources of anti-hypertensive agents.