- 作者： 羅新生
- 作者服務機構： 國防醫學院.寄生蟲及熱帶醫學系
- 中文摘要：
經過三個步驟之柱狀色層分離，痢疾原蟲之NADPH: flavin oxidoreductase已被純化。由膠體濾過法及SDS-聚
丙烯醯胺電泳法測定之分子量均為38,000-40,000，故知其次級結構為單一多胜鍊。此?對NADPH有高度之選擇性，但
對黃素之選擇性，則不顯著。由蔗糖梯度等電聚集法得知其等電點為7.8.酸鹼度及金屬離子，對此?之活性，均無甚大影
響。純化?之吸光光譜顯示，於450nm波長處，無吸光峰出現，證實此?，並非含黃素蛋白質。除各種黃素外，此?亦可
還原下列電子接受者：2.6-dichlorophenolindophenol，methylene blue，menadione，p-nitrobluetetrazolium，
cytochrome c，但是氧氣則不是其電子接受者。此?是由約360個膠基酸組成，其中三分之一是天門冬胺酸（或天門冬醯
胺酸）。此?能經過黃素氧化NADPH，於有氧情況下，生成過氧化氫，這個步驟，僅是化學反應，而不是?的作用。於痢
疾原蟲內，此氧化還原?扮演之角色，則可能是除去對痢疾原蟲有毒之氧氣。 - 英文摘要： Amebal NADPH: flavin oxidoreductase was purified to an apparent homogeneous state by three stepson column chromatography. A molecular weight of 38,000-40,000 was estimated by both gel filtration andsodium dodecyl sulfate polyacrylamide gel electrophoresis, indicating that the enzyme is composed of asingle polypeptide chain. The enzyme exhibits a high selectivity for NADPH but little or no selectivity withregard to flavin species. The enzyme has an isoelectric point of pH 7.8 as determined by sucrose gradientisoelectric focusing. It has no apparent pH optimum between pH 5.5-9.0 tested for its activity. Metal ionswere not required for the enzyme activity. The spectrum of purified enzyme exhibits no absorption peakat 450 nm, showing that it is not a flavoprotein. In the absence of flavins the purified enzyme is capable ofreducing a number of other electron acceptors, e.g., 2,6dichlorophenolindophenol, methylene blue, p-nitro-bluetetrazolium, menadione, cytochrome c, but not oxygen. Amebal flavin reductase is composed of ap-proximately 360 amino acid residues, one third of which are aspartic acid (or asparagine). The amebal flavinreductase mediates oxidation of NADPH via flavins. The formation of hydrogen peroxide by reduced flavinsin the presence of oxygen is non-enzymatic. Since oxygen is toxic to Entamoeba histolytica flavin reductasemay function as a scavenger for its removal.
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