Mas-Oliva Jaime, Delgado-Coello Blanca
Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Apartado Postal 70-243, 04510 México, D.F. Mexico.
Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Apartado Postal 70-243, 04510 México, D.F. Mexico.
Comp Biochem Physiol C Toxicol Pharmacol. 2007 Jul-Aug;146(1-2):207-213. doi: 10.1016/j.cbpc.2006.09.007. Epub 2006 Oct 21.
Cholesterol has been shown to regulate the activity of several membrane proteins. Although this phenomenon represents an important factor in the regulation of ion homeostasis, insights are needed to fully understand the role of this lipid in cell function in order to better comprehend the effect of bilayer components upon membrane function. Since evolution has shaped the composition of the membrane bilayer, it becomes of interest to study these changes in parallel with the many functions of membranes such as ion transport. The present study employing a plasma membrane preparation obtained from calf ventricular muscle demonstrates that cholesterol partially inhibits the Ca(2+),Mg(2+)-ATPase as the catalytic function of the calcium pump, when incubation reaction temperatures are below 42 degrees C. In contrast, when incubation reaction temperatures are above 42 degrees C, cholesterol apparently promotes enzyme stabilization reflected in higher activity. Although the activation energy values for the enzyme are almost the same at ranges between 15 and 40 degrees C, the use of elevated temperatures promote higher enzyme inactivation rates in control than in cholesterol enriched membranes. Cholesterol apparently is promoting stabilization that in turn protects the enzyme against thermal inactivation. This protective effect is reflected in a decrease of inactivation rate values and energy released during enzyme catalysis. The modification of many membrane properties throughout million of years made it possible for new evolutionary driving forces to show themselves as new characteristics in eukaryotes such as the one discussed in this study, dealing with the presence of cholesterol in the cell membrane directly associated to the promotion of protein thermostability.
胆固醇已被证明可调节多种膜蛋白的活性。尽管这一现象是调节离子稳态的一个重要因素，但仍需要深入了解这种脂质在细胞功能中的作用，以便更好地理解双层膜成分对膜功能的影响。由于进化塑造了膜双层的组成，因此结合膜的多种功能（如离子转运）来研究这些变化就变得很有意义。本研究采用从小牛心室肌获得的质膜制剂，结果表明，当孵育反应温度低于42℃时，胆固醇会部分抑制作为钙泵催化功能的Ca(2+),Mg(2+)-ATP酶。相反，当孵育反应温度高于42℃时，胆固醇显然会促进酶的稳定，表现为活性更高。尽管在15至40℃范围内酶的活化能值几乎相同，但与富含胆固醇的膜相比，在对照中使用较高温度会导致酶的失活速率更高。胆固醇显然在促进稳定，进而保护酶免受热失活。这种保护作用表现为失活速率值的降低以及酶催化过程中释放的能量的减少。在数百万年的时间里，许多膜特性的改变使得新的进化驱动力得以展现为真核生物中的新特征，比如本研究中所讨论的，细胞膜中胆固醇的存在与蛋白质热稳定性的提高直接相关。
