Sweet potato storage root trypsin inhibitor and their peptic hydrolysates exhibited angiotensin converting enzyme inhibitory activity in vitro

摘要

Trypsin inhibitor (TI), the root storage protein of sweet potato, was shown by spectrophotometric methods to inhibit angiotensin converting enzyme (ACE) in a dose-dependent manner (50-200 mu g/mL, with 31.9-53.2% inhibition) using N-[3-(2-furyl) acryloyl]-Phe-Gly-Gly (FAPGG) as a substrate. The 50% inhibition (IC_(50)) of ACE activity required 187.96 mu g/mL TI compared to 10 nM (868 ng/ mL) of Captopril. The use of TLC also showed TI as ACE inhibitor. TI acted as a mixed type inhibitor against ACE using FAPGG as a substrate. When 200 mu g/mL TI were added, Vmax and Km were, respectively 0.013 AA/min and 0.715 mM while without TI they were 0.027 AA/min and 0.419 raM. Pepsin was used for TI hydrolysis for different times. ACE inhibitory activity wasfound to increase from 34% to about 83% after 24 h of hydrolysis. The results suggested that when small peptides increased by pepsin hydrolysis of the TI ACE inhibitory capacity also increased up to 24 h and then decreased, it may be due to the disappearance of some conformational requirements. Ten peptides—namely HDHM, LR, SNIP, VRL, TYCQ, GTEKC, RF, YKAGE, AH and KIEL—were synthesized based on the simulated pepsin digestion of trypsin inhibitor and then tested for ACE inhibitory activity. IC_(50) values of individual peptides were 276.2, 746.4, 228.3, 208.6, 2.3, 275.8, 392.2, 141.56, 523.5 and 849.7 mu M, suggesting that TYCQ might represent the main active site for the ACE inhibition. TI and its hydrolysates might be good for control of hypertension and other diseases when people consume sweet potato tuberous roots.