Leikin A, Shinitzky M
Department of Membrane Research and Biophysics, Weizmann Institute of Science, Rehovot, Israel.
Biochim Biophys Acta. 1995 Apr 28;1256(1):13-7. doi: 10.1016/0005-2760(94)00244-s.
The delta 6-desaturase system was isolated from rat liver microsomes by high hydrostatic pressure (1500 bars) and the enzyme components were then separated by size chromatography. The lipids extracted by organic solvents from the pressure shed fractions were phosphatidylcholine (PC) and cholesterol at a mole ratio of 4:1. The acyl chains of the shed PC were 56% saturated and 21% polyunsaturated resulting predominantly from 13% higher and 15% lower contents of palmitic and arachidonic acid, respectively, as compared to those of microsomal PC. The weight ratio of phospholipids to protein in the shed desaturase fraction was 0.2 which corresponds to an average of 31 phospholipid molecules around each desaturase molecule. Differential scanning calorimetry of the lipids associated with the desaturase system showed a phase transition at 41 degrees C. Fluorescence anisotropy studies of the desaturase surrounding lipids indicated the same transition point. We concluded that the delta 6-desaturase has an associated lipid surrounding of PC and cholesterol at an approx. 4:1 mole ratio that constitutes a gel phase at physiological temperature. We suggest that this state is essential for optimal desaturase activity and that the specific acyl chains of the lipid annulus provide a regulatory sensor of the delta 6-desaturase activity.
通过高静水压（1500巴）从大鼠肝脏微粒体中分离出δ6-去饱和酶系统，然后通过尺寸色谱法分离酶组分。从压力释放级分中用有机溶剂提取的脂质是磷脂酰胆碱（PC）和胆固醇，摩尔比为4:1。释放的PC的酰基链56%为饱和脂肪酸，21%为多不饱和脂肪酸，与微粒体PC相比，棕榈酸和花生四烯酸的含量分别高出13%和低15%。释放的去饱和酶级分中磷脂与蛋白质的重量比为0.2，这相当于每个去饱和酶分子周围平均有31个磷脂分子。与去饱和酶系统相关的脂质的差示扫描量热法显示在41℃有一个相变。对去饱和酶周围脂质的荧光偏振研究表明了相同的转变点。我们得出结论，δ6-去饱和酶有一个以约4:1摩尔比存在的PC和胆固醇的相关脂质环境，在生理温度下构成凝胶相。我们认为这种状态对于最佳去饱和酶活性至关重要，并且脂质环的特定酰基链提供了δ6-去饱和酶活性的调节传感器。
