Identification of Three Novel Angiotensin-I-Converting Enzyme Inhibitory Peptides from Cassia Obtusifolia Seeds and Evaluation of their Inhibition Mechanisms

Angiotensin-I-converting enzyme inhibitory peptides were isolated from Cassia obtusifolia seeds by alcalase hydrolysis. Using ultrafiltration, the peptides were divided into four fractions (5 kDa). The fraction below 1 kDa exhibited the appropriate ACE inhibition (I[C.sub.50] = 65.88 [micro]g/mL), and was further purified by gel filtration chromatography, which displayed better angiotensin-I-converting enzyme inhibitory activity (I[C.sub.50] = 53.67 [micro]g/mL). The amino acid sequences of three novel angiotensin-I-converting enzyme inhibitory peptides were identified by liquid chromatography with tandem mass spectrometry as follows: IFPGCAN (I[C.sub.50] = 23.71 [micro]M), TEDFLTQ (I[C.sub.50] = 32.82 [micro]M), and GDEGSGGIIR (I[C.sub.50] = 18.21 [micro]M). Further experiments demonstrated that IFPGCAN and TEDFLTQ were competitive inhibitors, while GDEGSGGIIR was a noncompetitive inhibitor of the angiotensin-I-converting enzyme. Three peptides could form hydrogen bonds with the active site of the angiotensin-I-converting enzyme, according to molecular docking simulations of their interaction with the angiotensin-I-converting enzyme. Keywords: ACE inhibitory peptides; Angiotensin-I-converting enzyme; Cassia obtusifolia seeds; Identification; Molecular docking