Needham D, Evans E
Department of Pathology, University of British Columbia, Vancouver, Canada.
Biochemistry. 1988 Oct 18;27(21):8261-9. doi: 10.1021/bi00421a041.
We have used micromechanical tests to measure the thermoelastic properties of the liquid and gel phases of dimyristoylphosphatidylcholine (DMPC). We have found that the rippled P beta' phase is only formed when a vesicle is cooled to temperatures below the main acyl chain crystallization transition, Tc, under zero or very low membrane tension. We also found that the P beta' surface ripple or superlattice can be pulled flat under high membrane tension into a planar structure. For a ripple structure formed by acyl chains perpendicular to the projected plane, the projected area change that results from a flattening process is a direct measure of the molecular crystal angle. As such, the crystal angle was found to increase from about 24 degrees just below Tc to about 33 degrees below the pretransition. It was also observed that the P beta' superlattice did not form when annealed L beta' phase vesicles were heated from 5 degrees C to Tc; likewise, ripples did not form when the membrane was held under large tension during freezing from the L alpha phase. Each of these three procedures could be used to create a metastable planar structure which we have termed L*beta' since it is lamellar and plane-crystalline with acyl chains tilted to the bilayer plane. However, we show that this structure is not as condensed as the L beta' phase below 10 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)
我们使用微机械测试来测量二肉豆蔻酰磷脂酰胆碱（DMPC）液体和凝胶相的热弹性特性。我们发现，只有当囊泡在零或非常低的膜张力下冷却至低于主酰链结晶转变温度Tc时，才会形成波纹状的Pβ'相。我们还发现，在高膜张力下，Pβ'表面波纹或超晶格可以被拉平成平面结构。对于由垂直于投影平面的酰链形成的波纹结构，扁平化过程导致的投影面积变化是分子晶体角的直接度量。因此，发现晶体角从略低于Tc时的约24度增加到预转变温度以下的约33度。还观察到，当将退火的Lβ'相囊泡从5℃加热到Tc时，Pβ'超晶格未形成；同样，当膜在从Lα相冷冻过程中处于大张力下时，也不会形成波纹。这三个过程中的每一个都可用于创建一种亚稳平面结构，我们将其称为L*β'，因为它是层状且平面结晶的，酰链倾斜于双层平面。然而，我们表明，这种结构在低于10℃时不像Lβ'相那样致密。（摘要截断于250字）
