Read B D, McElhaney R N
J Bacteriol. 1975 Jul;123(1):47-55. doi: 10.1128/jb.123.1.47-55.1975.
The uptake of D-glucose by Acholeplasma laidlawii B occurs via a mediated transport process, as shown by the following observations: (i) glucose permeates A. laidlawii B cells at a rate at least 100 times greater than would be expected if its entry occurred only by simple passive diffusion; (ii) the apparent activation energy for glucose uptake in A. laidlawii is significantly lower than that expected and observed for the passive permeation of this sugar; (iii) glucose uptake appears to be a saturable process; (iv) glucose uptake can be completely inhibited by low concentrations of phloretin and phlorizin; and (v) glucose uptake is markedly inhibited at temperatures above 45 C, whereas the passive entry of erythritol continues to increase logarithmically until at least 60 C. The metabolism of D-glucose by this organism is rapid and, at low glucose concentrations, the intracellular radioactivity derived from D-[14-C]glucose is at any given time a reflection of the net effect of glucose transport, glucose metabolism, and loss from the cell of radioactive metabolic products. Care must thus be taken when attempting to determine the rate of glucose transport by measuring the accumulation by the cells of the total radioactivity derived from D-[14-C]glucose. The rate of uptake of D-glucose by A. laidlawii B cells is markedly dependent on the fatty acid composition and cholesterol content of the plasma membrane and exhibits a direct dependence on the fluidity of the membrane lipids as measured by their reversible, thermotropic gel to liquie-crystalline phase transition temperatures. In contrast to the transport rates, the apparent activation energy for glucose uptake above the phase transition temperature is not dependent on membrane lipid composition. At the temperature range within the membrane lipid phase transition region, the apparent activation energy of glucose uptake is different from the activation energy observed at temperatures above the phase transition. This may reflect the superimposed operation within the phase transition region of more than one temperature-dependent process.
莱氏无胆甾原体B对D - 葡萄糖的摄取是通过介导转运过程进行的，如下观察结果所示：（i）葡萄糖透过莱氏无胆甾原体B细胞的速率至少比仅通过简单被动扩散进入时预期的速率大100倍；（ii）莱氏无胆甾原体中葡萄糖摄取的表观活化能明显低于该糖被动渗透预期和观察到的活化能；（iii）葡萄糖摄取似乎是一个可饱和的过程；（iv）低浓度的根皮素和根皮苷可完全抑制葡萄糖摄取；（v）在45℃以上的温度下，葡萄糖摄取受到显著抑制，而赤藓醇的被动进入在至少60℃之前继续呈对数增加。该生物体对D - 葡萄糖的代谢很快，在低葡萄糖浓度下，任何给定时间源自D - [14 - C]葡萄糖的细胞内放射性是葡萄糖转运、葡萄糖代谢以及放射性代谢产物从细胞中损失的净效应的反映。因此，在试图通过测量细胞对源自D - [14 - C]葡萄糖的总放射性的积累来确定葡萄糖转运速率时必须小心。莱氏无胆甾原体B细胞对D - 葡萄糖的摄取速率明显取决于质膜的脂肪酸组成和胆固醇含量，并表现出对膜脂质流动性的直接依赖性，膜脂质流动性通过其可逆的热致凝胶到液晶相转变温度来测量。与转运速率相反，高于相转变温度时葡萄糖摄取的表观活化能不依赖于膜脂质组成。在膜脂质相转变区域内的温度范围内，葡萄糖摄取的表观活化能与在相转变温度以上观察到的活化能不同。这可能反映了在相转变区域内不止一个温度依赖性过程的叠加作用。
