Castuma C E, Brenner R R
Instituto de Investigaciones Bioquímicas de La Plata (INIBIOLP), CONICET-UNLP, Facultad de Ciencias Médicas, Argentina.
Biochem J. 1989 Mar 15;258(3):723-31. doi: 10.1042/bj2580723.
The relationship between lipid composition, the physical properties of microsomal phospholipids and the kinetics of liver UDP-glucuronyltransferase was studied in microsomes from guinea pigs supplied with a normal or a fat-free diet for 28 days. Fatty acid deficiency did not modify either the cholesterol/phospholipid molar ratio or the polar head group composition, but exclusively redistributed the unsaturated fatty acid pattern, by partially exchanging oleic for linoleic acid. This phenomenon accounts for the decrease of both rotational and translational mobilities of the fluorescent probes 1,6-diphenyl-1,3,5-hexatriene (DPH) and pyrene respectively. When the thermotropic behaviour of the different systems was assessed, no transition temperature (gel-liquid-crystalline) between 10 and 40 degrees C was seen as a consequence of the lower degree of unsaturation, either in the microsomal membranes or in the total lipid or total phospholipid extracts from the treated animals. In spite of this, the polarization ratio of trans-parinaric acid and the fluorescence intensity of merocyanine 540 revealed that a significant lateral phase separation occurred at 20-22 degrees C in the extracted phospholipids, which was smoother in the total lipid fractions and in the native microsomal membranes. Fatty acid deficiency caused an upward shift of the midpoint temperature of the lateral phase separation. Furthermore, the phosphatidylcholine extracted from the 'normal' microsomes showed a lateral phase separation centred at a lower temperature than that extracted from 'fat-deficient' microsomes. In contrast, the Arrhenius plot of UDP-glucuronyltransferase from 'normal' microsomes exhibited a change in slope at a higher temperature than that from treated microsomes. These results would suggest that fatty acid deficiency in guinea-pig liver microsomes, while rigidizing the bulk lipids, would segregate the most unsaturated phosphatidylcholine molecules towards the UDP-glucuronyltransferase microenvironment, in accordance with our previous results with cholesterol incorporation [Castuma & Brenner (1986) Biochemistry 25, 4733-4738].
研究了给豚鼠分别喂食正常饮食或无脂饮食28天后，微粒体中脂质组成、微粒体磷脂物理性质与肝脏UDP-葡糖醛酸基转移酶动力学之间的关系。脂肪酸缺乏并未改变胆固醇/磷脂摩尔比或极性头部基团组成，而是通过油酸与亚油酸的部分交换，专门重新分布了不饱和脂肪酸模式。这种现象分别导致荧光探针1,6-二苯基-1,3,5-己三烯（DPH）和芘的旋转和平动迁移率降低。当评估不同体系的热致行为时，由于不饱和程度较低，在微粒体膜、处理动物的总脂质或总磷脂提取物中，在10至40摄氏度之间均未观察到转变温度（凝胶-液晶态）。尽管如此，反式-紫黄质酸的偏振比和部花青540的荧光强度表明，在提取的磷脂中，20-22摄氏度时发生了明显的横向相分离，在总脂质部分和天然微粒体膜中这种相分离更平缓。脂肪酸缺乏导致横向相分离的中点温度上移。此外，从“正常”微粒体中提取的磷脂酰胆碱显示的横向相分离中心温度低于从“脂肪酸缺乏”微粒体中提取的磷脂酰胆碱。相反，“正常”微粒体中UDP-葡糖醛酸基转移酶的阿伦尼乌斯曲线在比处理过的微粒体更高的温度下出现斜率变化。这些结果表明，豚鼠肝脏微粒体中的脂肪酸缺乏，在使整体脂质刚性化的同时，会按照我们之前关于胆固醇掺入的结果[Castuma & Brenner (1986) Biochemistry 25, 4733-4738]，将最不饱和的磷脂酰胆碱分子隔离到UDP-葡糖醛酸基转移酶的微环境中。
