Leaver J, Alonso A, Durrani A A, Chapman D
Biochim Biophys Acta. 1983 Jan 19;727(2):327-35. doi: 10.1016/0005-2736(83)90418-2.
Acholeplasma laidlawii A has been grown in media containing synthetic, long chain C20- and C23-fatty acids possessing a diacetylene group in their acyl chains. Growth on the C23 diacetylenic acid was poor but was good on the C20 acid. Biosynthetic incorporation of the fatty acids occurs; as much as 90% of the membrane lipid fatty acyl chains consisting of the C20-diacetylenic fatty acid, the remainder being shorter chain, saturated fatty acids. The thermal phase transition of this biomembrane has been studied and a differential scanning calorimetry heating curve shows the presence of an endotherm corresponding to a membrane lipid phase transition occurring at about 26 degrees C. The lipid class composition of membranes containing the C20-diacetylene lipids was examined and found to be similar to membranes from cells grown on oleic acid-containing medium. (The ratio of monoglucosyl- to diglucosyldiacylglycerols was the same but the ratio of glycolipid to phosphatidylglycerol was higher in the cells grown with diacetylene fatty acids). Upon irradiation with ultraviolet light the cells and isolated biomembranes become coloured, either red or yellow depending upon their thermal history. The colour change indicates that extensive cross-linking of the lipids of the biomembranes of A. laidlawii has occurred and that a conjugated polymeric structure has been formed. Analysis of the extracted lipids from the biomembranes by GLC indicates that extensive cross-linking of the lipid chains within the biomembrane of a natural cell system has been achieved. The monoglucosyldiacylglycerols cross-link more readily that do the phosphatidylglycerol lipids. The effect of such lipid cross-linking or polymerisation on the activity at 35 degrees C of an intrinsic membrane-bound enzyme, NADH oxidase, and ribonuclease, an extrinsic membrane-bound enzyme, was studied. The NADH oxidase activity decreased rapidly upon cross-linking of the lipid environment whereas ribonuclease activity was unaffected. The potential for future studies of polymerised model and natural biomembranes is discussed.
赖氏无胆甾原体A已在含有合成的长链C20和C23脂肪酸的培养基中培养，这些脂肪酸在其酰基链中含有二乙炔基。在C23二乙炔酸上生长较差，但在C20酸上生长良好。脂肪酸发生生物合成掺入；多达90%的膜脂脂肪酸酰基链由C20 - 二乙炔脂肪酸组成，其余为较短链的饱和脂肪酸。对这种生物膜的热相变进行了研究，差示扫描量热法加热曲线显示存在一个吸热峰，对应于在约26℃发生的膜脂相变。检查了含有C20 - 二乙炔脂质的膜的脂质类别组成，发现其与在含油酸培养基上生长的细胞的膜相似。（单葡萄糖基二酰基甘油与双葡萄糖基二酰基甘油的比例相同，但在用二乙炔脂肪酸生长的细胞中糖脂与磷脂酰甘油的比例更高）。用紫外线照射后，细胞和分离的生物膜会变色，根据它们的热历史，颜色为红色或黄色。颜色变化表明赖氏无胆甾原体生物膜的脂质发生了广泛交联，并且形成了共轭聚合物结构。通过气相色谱法对从生物膜中提取的脂质进行分析表明，在天然细胞系统的生物膜内脂质链已实现广泛交联。单葡萄糖基二酰基甘油比磷脂酰甘油脂质更容易交联。研究了这种脂质交联或聚合对内在膜结合酶NADH氧化酶和外在膜结合酶核糖核酸酶在35℃时活性的影响。脂质环境交联后，NADH氧化酶活性迅速下降，而核糖核酸酶活性不受影响。讨论了聚合模型和天然生物膜未来研究的潜力。
