| 摘要: | 甘藷(Ipomoea batatas [L.] Lam 'Tainong 57')塊根胰蛋白酶抑制因子(TI)以(N-(3-[2-furyl] acryloyl)-Phe-Gly-Gly) (FAPGG)爲受質，利用分光光度計的方法分析抑制血管收縮素轉化酶(angiotensin converting enzyme, ACE)的能力，其效果隨劑量增加而增加（50到200μ/mL TI，分別抑制31.9-53.2%血管收縮素轉化醣活性）。TI對於血管收縮素轉化醣之50%抑制濃度(IC50)爲187.96μg/mL，對照組captopril爲10nM(868 ng/mL)。另外利用螢光silica TLC偵測FAPGG及其水解產物FAP，結果也顯示TI對於血管收縮素轉化醣有抑制的效果。TI對於血管收縮素轉化酶是屬於混合型抑制。而當加入200μg/mL TI時，Vmax和Km分別爲.013△A/min和0.715 mM；而未入TI時，Vmax和Km分別爲0.027△A/min和0.419 mM。利用胃蛋白酶以不同時間水解TI時，發現反應24小時時其血管收縮素轉化醣活性有抑制的效果可以從34%(0h)增加到83%(24h)。由結果可知小分子的胜肽會隨著水解時間增加且血管收縮素轉化酶活性抑制也有增加，但水解時間超過24h時，血管收縮素轉化醣活性抑制會降低，可能是由於一些勝肚的結構被破壞。利用電腦模擬胃蛋白酶水解TI的結果，十種人工合成具有抑制血管收縮素轉化醣活性胜肽：HDHM, LR, SNIP, VRL, TYCQ, GTEKC, RF, VKAGE, AH和KIEL，測定其IC50爲276.2, 746.4, 228.3, 208.6, 2.3, 275.8, 392.2, 141.56, 523.5和849.7μM。結果發現TYCQ具有很好的抑制血管收縮素轉化酶活性。當人們食用甘藷塊根時，胰蛋白酶抑制因子及其勝肚也許對於高血壓和其他疾病的控制是有益的。
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 (50-200μg/mL, with 31.9-53.2% inhibition) using N-[3-(2-furyl) acryloyl]-Phe-Gly-Gly (FAPGG) as a substrate. The 50% inhibition (IC50) of ACE activity required 187.96μg/mL TI compared to 10nM (868ng/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 200μg/mL TI were added, Vmax and Km were, respectively 0.013 ΔA/min and 0.715mM while without TI they were 0.027ΔA/min and 0.419mM. Pepsin was used for TI hydrolysis for different times. ACE inhibitory activity was found to increase from 34% to about 83% after 24h of hydrolysis. The results suggested that when small peptides increased by pepsin hydrolysis of the TI ACE inhibitory capacity also increased up to 24h and then decreased, it may be due to the disappearance of some conformational requirements. Ten peptides-namely HDHM, LR, SNIP, VRL, TYCQ, GTEKC, RF, VKAGE, AH and KIEL-were synthesized based on the simulated pepsin digestion of trypsin inhibitor and then tested for ACE inhibitory activity. IC50 values of individual peptides were 276.2, 746.4, 228.3, 208.6, 2.3, 275.8, 392.2, 141.56, 523.5 and 849.7μM, 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. |
