就我們先前報告表示，甘藷胰蛋白酶抑制因子(SPTI)具有去氫抗壞血酸還原酶和單去氫抗壞血酸還原酶活性，且SPTI也具有了抗氧化活性可對抗不同自由基、抑制細胞生長和誘導細胞凋亡。因此，我們本篇文章研究SPTI是否具有抗氧化相關酵素的活性。以純化的SPTI發現其具有類似硫基轉移酶(thioltransferase, TTase)的活性，其比活性在pH7.5和8.5時分別為1.6±0.3 and 0.58±0.02 nmol/min/mg，並以大豆胰蛋白酶抑制因子(STI)作為控制組。且純化的SPTI也發現其具有類似穀胱甘肽S-轉移酶(glutathione S-transferase, GSTs)的活性，其比活性在pH6.0和7.0時分別為0.094±0.005和0.43±0.03 μmol/min/mg。利用SPTI雙硫鍵附近的胺基酸(Cys153~Cys160)與已發表之TTase和GST序列比較，結果顯示SPTI具有類似硫基轉移酶和穀胱甘肽S-轉移酶的活性主要的理由是其分子序列相似。
Our previous reports showed that sweet potato trypsin inhibitor (SPTI) exhibited both dehydroascorbate reductase and monodehydroascorbate reductase activities. SPTI also exhibited antioxidant activities against different radicals, inhibited growth of NB4 cells, and induced apoptosis of NB4 cells. In this work, we found novel enzyme activities of SPTI. The purified SPTI had thioltransferase (TTase)-like activity with a specific activity of 1.6±0.3 and 0.58±0.02 nmol/min/mg at pH 7.5 and 8.5, respectively. Soybean TI (STI) was used as a positive control. The purified SPTI also had glutathione S-transferase (GST)-like activity with a specific activity of 0.094±0.005 and 0.43±0.03 μmol/min/mg at pH 6.0 and 7.0, respectively. The amino acids around disulfide bond of SPTI (Cys153~Cys160) were compared with those of published TTase and GST. The results provide a chemically and physiologically reasonable molecular basis on which SPTI exhibits both TTase-like and GSTs-like activities.
