Isolation, purification and characterisation of angiotensin <scp>I</scp>‐converting enzyme–inhibitory peptides derived from catfish (<i><scp>C</scp>larias batrachus</i>) muscle protein thermolysin hydrolysates

Abstract

Summary The angiotensin I‐converting enzyme ( ACE )‐inhibitory activities of catfish ( C larias batrachus ) muscle protein hydrolysates were investigated. Thermolytic digests of C . batrachus sarcoplasmic and myofibrillar proteins exhibited inhibitory activity towards ACE and were purified with the aim of ultrafiltration, gel filtration and reversed‐phase high‐performance liquid chromatography ( RP ‐ HPLC ). The amino acid sequences of hydrolysates with the highest ACE ‐inhibitory activities were determined using electrospray quadrupole time‐of‐flight tandem mass spectrometry ( ESI ‐ TOFQ MS / MS ). The sequences of GPPP ( IC 50 = 0.86 μ m ) and IEKPP ( IC 50 = 1.2 μ m ) corresponding to the fragments 986–989 and 441–445 of myosin‐ I heavy chain were identified for the sarcoplasmic and myofibrillar protein hydrolysates, respectively. Peptide GPPP exhibited a mixed‐type inhibition whereas peptide IEKPP could only bind to the active sites of ACE . The results demonstrate that hydrolysates of C . batrachus muscle proteins obtained by thermolysin may contain bioactive peptides.