Pokorny A, Almeida P F, Vaz W L
Departamento de Química, Universidade de Coimbra, 3004-535 Coimbra, Portugal.
Biophys J. 2001 Mar;80(3):1384-94. doi: 10.1016/S0006-3495(01)76111-5.
The effects of solid-fluid phase separations on the kinetics of association of a single-chain fluorescent amphiphile were investigated in two different systems: pure DMPC (dimyristoylphosphatidylcholine) and a 1:1 mixture of DMPC and DSPC (distearoylphosphatidylcholine). In pure DMPC vesicles, solid (s) and fluid (l(d)) phases coexist at the phase transition temperature, T(m), whereas a 1:1 mixture of DMPC and DSPC shows a stable s-l(d) phase separation over a large temperature interval. We found that in single-component bilayers, within the main phase transition, the experimental kinetics of association are clearly not single-exponential, the deviation from that function becoming maximal at the T(m). This observation can be accounted for by a rate of desorption that is slower than desorption from either fluid or solid phases, leaving the rates of insertion unchanged, but a treatment in terms of stable fluid and solid domains may not be adequate for the analysis of the association of an amphiphile with pure DMPC vesicles at the T(m). In DMPC/DSPC mixtures with solid-fluid phase coexistence, association occurs overall faster than expected based on phase composition. The observed kinetics can be described by an increase in the rate of insertion, leaving the desorption rates unchanged. The fast kinetics of insertion of the amphiphile into two-phase bilayers in two-component vesicles is attributed to a more rapid insertion into defect-rich regions, which are most likely phase boundaries between solid and fluid domains. A two-component mixture of lipids that shows a stable phase separation between l(d)-s phases over a large temperature interval thus behaves very differently from a single-component bilayer at the T(m), with respect to insertion of amphiphiles.
在两个不同的体系中研究了固-液相分离对单链荧光两亲分子缔合动力学的影响：纯二肉豆蔻酰磷脂酰胆碱（DMPC）以及DMPC与二硬脂酰磷脂酰胆碱（DSPC）的1:1混合物。在纯DMPC囊泡中，固相（s）和液相（l(d)）在相变温度T(m)下共存，而DMPC与DSPC的1:1混合物在较大的温度区间内呈现稳定的s-l(d)相分离。我们发现，在单组分双层膜中，在主要相变过程中，缔合的实验动力学明显不是单指数的，在T(m)时与该函数的偏差最大。这种观察结果可以用比从液相或固相中解吸慢的解吸速率来解释，插入速率不变，但用稳定的流体和固体域来分析两亲分子与纯DMPC囊泡在T(m)时的缔合可能并不充分。在具有固-液相共存的DMPC/DSPC混合物中，总体上缔合比基于相组成预期的要快。观察到的动力学可以用插入速率的增加来描述，解吸速率不变。两亲分子快速插入双组分囊泡中的两相双层膜归因于更快速地插入富含缺陷的区域，这些区域很可能是固体和流体域之间的相界。因此，在较大温度区间内显示出l(d)-s相之间稳定相分离的脂质双组分混合物，在两亲分子插入方面，其行为与T(m)时的单组分双层膜非常不同。
