Angiotensin-I-converting enzyme (ACE) inhibitory peptides derived from marine organism have shown a blood pressure lowering effect with no side effects. A new affinity medium of Fe3O4@ZIF-90 immobilized ACE (Fe3O4@ZIF-90-ACE) was prepared and used in the purification of ACE inhibitory peptides from Wakame (Undaria pinnatifida) protein hydrolysate (<5 kDa). The Fe3O4@ZIF-90 nanoparticles were prepared by a one-pot synthesis and crude ACE extract from pig lung was immobilized onto it, which exhibited excellent stability and reusability. A novel ACE inhibitory peptide, KNFL (inhibitory concentration 50, IC50 = 225.87 μM) was identified by affinity purification using Fe3O4@ZIF-90-ACE combined with reverse phase-high performance liquid chromatography (RP-HPLC) and MALDI-TOF mass spectrometry. Lineweaver-Burk analysis confirmed the non-competitive inhibition pattern of KNFL, and molecular docking showed that it bound at a non-active site of ACE via hydrogen bonds. This demonstrates that affinity purification using Fe3O4@ZIF-90-ACE is a highly efficient method for separating ACE inhibitory peptides from complex protein mixtures and the purified peptide KNFL could be developed as a functional food ingredients against hypertension.
Keywords: affinity purification; angiotensin converting enzyme inhibitory peptides; immobilization; magnetic zeolitic imidazolate framework.