Identification of a novel ACE-inhibitory peptide from casein and evaluation of the inhibitory mechanisms

Various bioactive peptides are continuously being identified from casein hydrolysates. In this work, a novel angiotensin I-converting enzyme (ACE)-inhibitory (ACEI) peptide, NMAINPSKENLCSTFCK, derived from the alpha(s2)-casein fragment residues 25-41, was screened and identified by UPLC-ESI-Q-TOF-MS/MS from tryptic casein hydrolysate. The IC50 value of the peptide, determined by an HPLC method, was 129.07 mu M. The Lineweaver-Burk plot showed that this peptide acted as a mixed-type inhibitor against ACE, which might be attributed to the peptide being susceptible to degradation by ACE, indicating that the mixed-type inhibition could partly be a result of newly generated peptide fragments. The physicochemical characteristics and the secondary structure were evaluated by circular dichroism analysis and online prediction software (Expasy, PepDraw, and ProtParam) to identify the basic characteristics of this peptide. Moreover, molecular docking was simulated by Discovery Studio 2017 R2 software to provide the potential mechanisms underlying the ACEI activity of the peptides.