Senak L, Mendelsohn R
Department of Chemistry, Newark College of Arts and Science, Rutgers University, New Jersey 07102.
Biochemistry. 1993 Jun 22;32(24):6288-94. doi: 10.1021/bi00075a024.
CaATPase from rabbit sarcoplasmic reticulum (SR) has been isolated, purified, and reconstituted into unilamellar vesicles with 1,2-dipentadecanoylphosphatidylcholine (DPePC) and acyl-chain-perdeuterated 1,2-dipalmitoylphosphatidylcholine (DPPC-d62). For total lipid:protein mole ratios between 25 and 70, a constant "hard-to-exchange" phospholipid population (HEPP) of 12 +/- 4 native phospholipid molecules per protein monomer is observed, consistent with the studies of Bick et al. [(1991) Arch. Biochem. Biophs. 286, 346-352]. Thermotropic and conformational properties of the lipids in native SR and in the reconstituted systems were probed with FT-IR spectroscopy. The native SR phospholipids undergo a broad phase transition centered at about 1-2 degrees C and are thus disordered under physiological conditions. The thermotropic behavior of CH2 wagging progressions characteristic of the palmitate chains differs from that of the total lipid population and is suggestive of membrane microheterogeneity. The individual thermotropic and conformational properties of the HEPP and the exogenous lipid in reconstituted vesicles containing CaATPase and DPPC-d62 were monitored. At temperatures below the onset of the gel-liquid-crystal phase transition, the HEPP possesses significant conformational disorder, and exhibits the monotonic introduction of gauche rotamers as the temperature is raised from -55 to 27 degrees C, in contrast to the exogenous lipid, which exhibits a constant high order over the same temperature range. Nevertheless, the HEPP undergoes a residual order-disorder phase transition with similar but not identical parameters (half-width, midpoint temperature) to the gel-liquid-crystal transition of the bulk (exogenous) lipid in the reconstituted systems.(ABSTRACT TRUNCATED AT 250 WORDS)
兔肌浆网（SR）的CaATPase已被分离、纯化，并与1,2 - 二戊酰磷脂酰胆碱（DPePC）和酰基链全氘代的1,2 - 二棕榈酰磷脂酰胆碱（DPPC - d62）一起重构成单层囊泡。对于总脂质与蛋白质的摩尔比在25至70之间的情况，观察到每个蛋白质单体有12±4个天然磷脂分子的恒定“难交换”磷脂群体（HEPP），这与Bick等人的研究一致[（1991年）《生物化学与生物物理学文献》286, 346 - 352]。用傅里叶变换红外光谱法探究了天然SR和重构系统中脂质的热致和构象性质。天然SR磷脂经历以约1 - 2℃为中心的宽相变，因此在生理条件下是无序的。棕榈酸链特有的CH2摇摆跃迁的热致行为与总脂质群体不同，提示膜的微不均匀性。监测了含有CaATPase和DPPC - d62的重构囊泡中HEPP和外源性脂质各自的热致和构象性质。在低于凝胶 - 液晶相转变起始温度时，HEPP具有显著的构象无序，并且随着温度从 - 55℃升高到27℃，呈现出gauche旋转异构体的单调引入，这与外源性脂质不同，后者在相同温度范围内表现出恒定的高有序性。然而，HEPP经历了一个残余的有序 - 无序相变，其参数（半高宽、中点温度）与重构系统中大量（外源性）脂质的凝胶 - 液晶转变相似但不完全相同。（摘要截断于250字）
