Isolation of Human Renin Inhibitor from Soybean: Soyasaponin I Is the Novel Human Renin Inhibitor in Soybean

We found human renin inhibitory activity in soybean and isolated the active compound, soybean renin inhibitor (SRI). The physico-chemical data on the isolated SRI were identical with those of soyasaponin I. SRI showed significant inhibition against recombinant human renin, with an IC50 value of 30 mu g/ml. Kinetic studies with SRI indicated partial noncompetitive inhibition, with a K-i value of 37.5 mu M. On the other hand, SRI weakly inhibited pepsin, papain, and brome-line activities, but did not inhibit other proteinases, such as trypsin, kallikrein, angiotensin converting enzyme, and aminopeptidase M. Moreover, a significant (p < 0.05) decrease in the systolic blood pressure of spontaneously hypertensive rats was observed when partially purified SRI was orally administrated at 40 mg/kg/d for 7 weeks. This is the first demonstration of a renin inhibitor from soybean, soyasaponin I.