Both dioscorin, the tuber storage protein of yam (Dioscorea alata cv. Tainong No. 1), and its peptic hydrolysates exhibited angiotensin converting enzyme inhibitory activities

Dioscorin, the tuber storage protein of yam (Dioscorea alata cv. Tainong No. 1), was purified to homogeneity by DE-52 ion-exchange chromatography. This purified dioscorin was shown by spectrophotometric methods to inhibit anglotensin converting enzyme (ACE) in a dose-dependent manner (12.5-750 mug, respectively, 20.83-62.5% inhibitions) using N-[3-(2-furyl)acryloyl]-Phe-Gly-Gly (FAPGG) as substrates. The 50% inhibition (IC50) of ACE activity was 6.404 muM dioscorin (250 mug corresponding to 7.81 nmol) compared to that of 0.00781 muM (0.0095 nmol) for captopril. The commercial bovine serum albumin and casein (bovine milk) showed less ACE inhibitory activity. The use of qualitative TLC also showed dioscorin as ACE inhibitors. Dioscorin showed mixed noncompetitive inhibitions against ACE; when 31.25 mug of dioscorin (0.8 muM) was added, the apparent inhibition constant (K-i) was 2.738 muM. Pepsin was used for dioscorin hydrolysis at 37 degreesC for different times. It was found that the ACE inhibitory activity was increased from 51.32% to about 75% during 32 In hydrolysis. The smaller peptides were increased with increasing pepsin hydrolytic times. Dioscorin and its hydrolysates might be a potential for hypertension control when people consume yam tuber.