Connolly T J, Carruthers A, Melchior D L
J Biol Chem. 1985 Mar 10;260(5):2617-20.
The influence of altered bilayer cholesterol content on the catalytic activity of the human red cell hexose transporter was examined by reconstitution of the transport protein (band 4.5) into bilayers of large unilamellar vesicles formed from dipalmitoyl lecithin and varying amounts of cholesterol. The physical state of the bilayers was characterized by differential scanning calorimetry. The major findings are as follows: changes in bilayer phase behavior occur at membrane cholesterol levels of 15 to 20 mol % and 30 to 40 mol %; and the catalytic activity of the reconstituted transporter (Vmax/transporter) correlates with bilayer phase behavior. In crystalline bilayers, this is seen as an abrupt, stimulation of activity at 15 mol % cholesterol (which is reversed at 17.5 mol %) and a gradual acceleration of activity between 30 to 40 mol % cholesterol. In fluid bilayers (where activity is high), activity is unaffected by 10, 20, and 30 mol % cholesterol. However, 12.5 and 17.5 mol % cholesterol reduce activity by 100-fold. These studies demonstrate that small changes in bilayer cholesterol content result in drastic alterations in transporter activity. Transporter sensitivity to cholesterol is a complex rather than monotonic function of bilayer cholesterol content and appears to be primarily determined by bilayer composition rather than by bilayer "fluidity."
通过将转运蛋白（4.5 带）重组到由二棕榈酰卵磷脂和不同量胆固醇形成的大单层囊泡双层中，研究了双层胆固醇含量改变对人红细胞己糖转运体催化活性的影响。通过差示扫描量热法对双层的物理状态进行了表征。主要发现如下：双层相行为的变化发生在膜胆固醇水平为 15%至 20%摩尔和 30%至 40%摩尔时；重组转运体的催化活性（Vmax/转运体）与双层相行为相关。在结晶双层中，这表现为在胆固醇含量为 15%摩尔时活性突然受到刺激（在 17.5%摩尔时逆转），以及在胆固醇含量为 30%至 40%摩尔之间活性逐渐加速。在流体双层中（活性较高），10%、20%和 30%摩尔的胆固醇对活性没有影响。然而，12.5%和 17.5%摩尔的胆固醇会使活性降低 100 倍。这些研究表明，双层胆固醇含量的微小变化会导致转运体活性发生剧烈改变。转运体对胆固醇 的敏感性是双层胆固醇含量的复杂而非单调函数，似乎主要由双层组成而非双层“流动性”决定。
