Purification and identification of an angiotensin I-converting enzyme inhibitor from soy sauce

The inhibitory activity of an angiotensin I-converting enzyme (ACE) detected in soy sauce was fractionated into two major fractions of high molecular weight (Hw) and low molecular weight (Lw) by gel filtration chromatography on Bio-gel P-2 after treating with ethanol. The Hw fraction reduced the blood pressure in hypertensive rats after orally administering, while the Lw fraction did not. The ACE inhibitor in the Hw fraction was further purified by Dowex 50W ion-exchange chromatography and four subsequent steps of HPLC. On the basis of the SIMS-mass spectrum, NMR spectrum and other characteristics, the purified ACE inhibitor was identified as nicotianamine (N-[N-(3-amino-3-carboxypropyl)-3-amino-3- carboxypropyl]azetidine-2-carboxylic acid). The IC 50 value for this ACE was 0.26 µM.