ACE inhibitory activity
in soy sauce was fractionated into two major fractions
of high molecular weight (Hw) and low molecular weight
(Lw) by gel filtration chromatography after treating with
ethanol. The Hw fraction decreased blood pressure in hypertensive
rats after oral administration, while the Lw fraction
did not (Table 1). Blood pressure decreased 1–8 h after
the administration of the Hw fraction and returned to the
baseline level within 24 h in spontaneously hypertensive rats
(SHR) and two-kidney Goldblantt hypertensive rats (2KGH
rats). The Lw fraction had no effect on blood pressure in
either type of rat. The main ACE inhibitor in the Hw fraction
was purified by high-performance liquid chromatography
and was identified as nicotianamine (N-[N-(3-amino-
3-carboxypropyl)-3-amino-3-carboxypropyl]-azetidine-2-carboxylic
acid) (Fig. 1). The IC50 of nicotianamine for ACE
was 0.26 µM. It was one-tenth of that of the widely used
antihypertensive drug Captopril.