Serrano R, Reeves R E
Biochem J. 1974 Oct;144(1):43-8. doi: 10.1042/bj1440043.
That the uptake of glucose by the parasitic amoeba Entamoeba histolytica occurs by an equilibrative transport system is supported by the following observations. 1. The rate of glucose uptake is several orders of magnitude greater than the uptake by pinocytosis. 2. The uptake of glucose exhibits saturation kinetics, with K(m)=1.6mm and V(max.) ranging from 2 to 5mumol/min per ml of cells at 37 degrees C. 3. The glucose analogues 2-deoxyglucose, 3-O-methylglucose and d-xylose are transported by the glucose system although with much less affinity. Competitive inhibition was observed between pairs of substrates, with K(i) values for any sugar closely coincident with the corresponding K(m). 4. d-Xylose, a sugar not metabolized by the cells, equilibrated with 80% of the amoebal cell water. 5. Cells equilibrated with xylose exhibited countertransport of this sugar against its concentration gradient when another substrate was added to the medium. 6. Blocking of glycolysis by iodoacetate or F(-) has no immediate effect on transport. The presence of a glucose-transport system in E. histolytica contrasts with the situation found in the non-parasitic amoeba, where pinocytosis seems to be the only mechanism of solute uptake.
以下观察结果支持寄生性变形虫溶组织内阿米巴通过平衡转运系统摄取葡萄糖这一观点。1. 葡萄糖的摄取速率比胞饮作用的摄取速率高几个数量级。2. 葡萄糖的摄取呈现饱和动力学，在37℃时，K(m)=1.6mmol，V(max.)为每毫升细胞2至5μmol/分钟。3. 葡萄糖类似物2-脱氧葡萄糖、3-O-甲基葡萄糖和D-木糖可通过葡萄糖系统转运，尽管亲和力低得多。观察到底物对之间存在竞争性抑制，任何一种糖的K(i)值与相应的K(m)值非常接近。4. D-木糖是一种细胞不能代谢的糖，它与80%的变形虫细胞内水达到平衡。5. 当向培养基中添加另一种底物时，用木糖平衡的细胞会出现这种糖逆浓度梯度的反向转运。6. 碘乙酸盐或F(-)阻断糖酵解对转运没有立即影响。溶组织内阿米巴存在葡萄糖转运系统，这与非寄生性变形虫的情况形成对比，在非寄生性变形虫中，胞饮作用似乎是溶质摄取的唯一机制。
