The synthetic Angiotensin Converting Enzyme (ACE) inhibitors have side effects and hence demands for natural ACE inhibitors have been rising. The aim of this study is to purify and introduce natural ACE inhibitors extracted from Zizyphus jujuba fruits. Proteins from Zizyphus jujuba were lysed by trypsin, papain and their combination. Acquired peptides were purified and evaluated for ACE inhibitory activity. Peptide fractions with inhibitory activity were sequenced using tandem mass spectrometry. To elucidate the mode of peptide binding to ACE, homology modeling, molecular docking and molecular dynamics simulation were performed. Amino acid sequence of F2 and F4 peptides, which were the most active hydrolysates, were determined to be IER and IGK with the IC 50 values of 0.060 and 0.072 mg/ ml, respectively. Results obtained by computational analysis revealed that similar to the common ACE competitive inhibitors such as captopril, IER tripeptide binds to the enzyme active site, in vicinity of the zinc binding site, and occupies the S1 and S2' subsites. Binding occurs through hydrogen bonding with Gln293, Lys522, His524, Tyr531 and also several hydrophobic interactions. Collectively, these findings indicate that IER tripeptide inhibits the rabbit ACE enzyme through a competitive mechanism of inhibition with IC 50 values in the millimolar range.Angiotensin converting enzyme (ACE) inhibitors are a new class of drugs which are critical in the treatment of hypertension and heart failure 1 . Although the synthetic drugs are often prescribed due to their well-known role and convenience of access, they have undesirable effects, such as extreme low blood pressure, cough, bad tastes and allergic reactions. Contrariwise, natural inhibitors regulate hypertension under mild conditions without significant side effects; hence, they can be considered as worthy alternatives to synthetic drugs 2 .ACE inhibitory peptides are the best known amongst various classes of regulatory bioactive peptides due to the development of functional foods with homeostasis role in the human body 3 . ACE is a Zn-metallopeptidase that removes a dipeptide from the decapeptide angiotensin-I to produce the potent vasoconstriction octapeptide angiotensin-II 4 . Several peptides originated from animal or plant proteins exhibit significant therapeutic/ regulatory performances like antihypertensive, antimicrobial, antioxidant, immunoregulatory, anticancer activities, etc 3 .Investigations to find more bioactive peptides, especially multifunctional ones have attracted the attention of researchers. The bioactive peptides are often inactive in their natural forms and when released by enzymatic hydrolysis, display their biological activity 3,5 . So far, several ACE inhibitory peptides have been reported from hydrolysis of different food proteins, such as hen egg white lysozyme 4 , fish 6 , corn 7 , soybean 8 , milk 9 , casein 10 , etc. These peptides are good candidates to regulate blood pressure and also to balance fluid and electrolytes in mammals.
Scientific Rep...