Macdonald P M, Sykes B D, McElhaney R N
Biochemistry. 1985 May 7;24(10):2412-9. doi: 10.1021/bi00331a004.
The hydrocarbon chain orientational order parameters of membranes of Acholeplasma laidlawii B enriched with large quantities of a linear saturated, a methyl iso-branched, or a methyl anteiso-branched fatty acid plus small quantities of various isomeric monofluoropalmitic acid probes were determined via fluorine-19 nuclear magnetic resonance spectroscopy (19F NMR) over a range of temperatures spanning the gel to liquid-crystalline phase transitions (determined by differential scanning calorimetry). Membrane orientational order profiles in the liquid-crystalline state were generally similar regardless of the particular fatty acyl structure, showing a region of relatively constant order preceding a region of progressive decline in order toward the methyl terminus of the acyl chain. In the gel state, the order profile of the linear saturated fatty acid enriched membranes was characteristically flat, with little head to tail gradation of order. In contrast, the methyl iso-branched and the methyl anteiso-branched enriched membranes exhibited a local disordering in the gel phase reflected in a very pronounced head to tail gradient of order, which remained at temperatures below the lipid phase transition. In addition, the methyl iso- and anteiso-branched fatty acid enriched membranes were overall more disordered than the membrane containing only linear saturated fatty acyl groups. Thus, at a constant value of reduced temperature below the lipid phase transition, overall order decreased in the progression 15:0 greater than 16:0i greater than 16:0ai, suggesting that these methyl-branched substituents lower the lipid phase transition by disrupting the gel phase lipid chain packing.(ABSTRACT TRUNCATED AT 250 WORDS)
通过氟 - 19核磁共振光谱法（19F NMR），在跨越凝胶态到液晶态相变的一系列温度范围内（由差示扫描量热法测定），测定了富含大量线性饱和脂肪酸、甲基异支链脂肪酸或甲基反异支链脂肪酸以及少量各种异构单氟棕榈酸探针的莱氏无胆甾原体B膜的烃链取向有序参数。无论特定的脂肪酰基结构如何，液晶态下的膜取向有序分布通常相似，在酰基链甲基末端方向上，有序度逐渐下降的区域之前有一个相对有序度恒定的区域。在凝胶态下，富含线性饱和脂肪酸的膜的有序分布特征是平坦的，从头到尾的有序度几乎没有梯度变化。相比之下，富含甲基异支链和甲基反异支链脂肪酸的膜在凝胶相中表现出局部无序，这反映在从头到尾非常明显的有序度梯度上，并且在低于脂质相变的温度下仍然存在。此外，富含甲基异支链和反异支链脂肪酸的膜总体上比仅含有线性饱和脂肪酰基的膜更无序。因此，在低于脂质相变的恒定降低温度值下，总体有序度在15:0大于16:0i大于16:0ai的顺序中降低，这表明这些甲基支链取代基通过破坏凝胶相脂质链堆积来降低脂质相变温度。（摘要截断于250字）
