Monck M A, Bloom M, Lafleur M, Lewis R N, McElhaney R N, Cullis P R
Department of Biochemistry, University of British Columbia, Vancouver, Canada.
Biochemistry. 1993 Mar 30;32(12):3081-8. doi: 10.1021/bi00063a020.
Recent investigations have indicated that there exists a well-defined range of membrane hydrocarbon order compatible with good growth of the microorganism Acholeplasma laidlawii B [Monck, M., Bloom, M., Lafleur, M., Lewis, R. N. A. H., McElhaney, R. N., & Cullis, P. R. (1992) Biochemistry 31, 10037-10043]. Since cholesterol increases hydrocarbon order in membranes, it was of interest to examine the effect of cholesterol on the hydrocarbon order and growth characteristics of A. laidlawii B. Cholesterol is normally absent from A. laidlawii membranes since it is neither biosynthesized nor required for the growth or survival of the microorganism. However, cholesterol will be incorporated into the membrane if exogenously supplied to the A. laidlawii culture. For membranes prepared from cells grown in the presence of cholesterol, chemical determinations indicated cholesterol represented as much as 40 mol% of the total membrane lipid. However, 2H NMR order parameter measurements and DSC studies of the same membrane preparation suggested that cholesterol was present at significantly lower levels (approximately 10-15 mol%) in the membrane lipid bilayer. Further incorporation of cholesterol into the A. laidlawii lipid bilayer was found to occur with an increase in temperature or by lyophilization and rehydration at high temperatures, suggesting that sterol present in a separate pool in the membrane preparation could then gain access to the bilayer. 2H NMR spectra of A. laidlawii membrane preparations containing deuterium-labeled cholesterol indicate that the bulk of the cholesterol present in this separate pool is in a solid form.
最近的研究表明，存在一个明确界定的膜烃有序范围，该范围与莱氏无胆甾原体B的良好生长相兼容[蒙克，M.，布鲁姆，M.，拉弗勒，M.，刘易斯，R.N.A.H.，麦克尔哈尼，R.N.，&卡利斯，P.R.（1992年）《生物化学》31卷，10037 - 10043页]。由于胆固醇会增加膜中的烃有序度，因此研究胆固醇对莱氏无胆甾原体B的烃有序度和生长特性的影响很有意义。莱氏无胆甾原体的膜中通常不存在胆固醇，因为它既不进行生物合成，微生物的生长或存活也不需要它。然而，如果向莱氏无胆甾原体培养物中额外提供胆固醇，它将被整合到膜中。对于在胆固醇存在下生长的细胞制备的膜，化学测定表明胆固醇占总膜脂的比例高达40摩尔%。然而，对同一膜制剂进行的2H NMR有序参数测量和差示扫描量热法研究表明，胆固醇在膜脂双层中的含量明显较低（约10 - 15摩尔%）。发现随着温度升高或通过高温冻干和再水化，胆固醇会进一步整合到莱氏无胆甾原体的脂双层中，这表明膜制剂中存在于单独池中的甾醇随后可以进入双层。含有氘标记胆固醇的莱氏无胆甾原体膜制剂的2H NMR光谱表明，存在于这个单独池中的大部分胆固醇是固态的。
