Castuma C E, Brenner R R
Biochim Biophys Acta. 1983 Mar 23;729(1):9-16. doi: 10.1016/0005-2736(83)90449-2.
The effect of fat deprivation on microsomal membrane fluidity of guinea-pig livers and the kinetic cooperativity of UDP-glucuronyl transferase towards its natural substrate, the UDP-glucuronic acid, were studied. Fat deprivation in the diet of weanling guinea-pigs evoked a typical essential fatty-acid-deficient pattern in the composition of the microsomal membrane. The unsaturated:saturated fatty acid ratio progressively declined in the membrane during the 21-day period tested. This decline determined a gradual increase in the fluorescence anisotropy (rs) of the membrane labeled with diphenylhexatriene and the apparent microviscosity of the lipid bilayer calculated from these values increased from 1.1 to 1.8 poise. In addition, when the infinitely slow decaying fluorescence anisotropy ((r infinity), which is proportional to the square of the lipid order parameter, was calculated from rs data, a significant increase in these parameters was also obtained. Furthermore, this decrease of the double bond index:saturated acid ratio of the membrane was associated with a parallel increase in Hill coefficients of the UDP-glucuronyl transferase that gradually lost the negative homotropic effect and cooperativity of UDP-glucuronic acid. The Hill coefficient varied from 0.39 to 0.98 during the 21-day period studied. Our observations indicate on one side that changes in the fat composition of the diet are accompanied by modifications in the lipid composition and fluidity of the microsomal membrane, and the apparent cooperativity of the enzyme. On the other side, they suggest that the evaluation of Hill coefficients of UDP-glucuronyl transferase might be used as a sensitive test to investigate conformational changes in the microsomal membrane of the liver.
研究了脂肪剥夺对豚鼠肝脏微粒体膜流动性以及UDP - 葡糖醛酸基转移酶对其天然底物UDP - 葡糖醛酸的动力学协同性的影响。断奶豚鼠饮食中的脂肪剥夺在微粒体膜组成中引发了典型的必需脂肪酸缺乏模式。在所测试的21天期间，膜中不饱和脂肪酸与饱和脂肪酸的比例逐渐下降。这种下降导致用二苯基己三烯标记的膜的荧光 anisotropy（rs）逐渐增加，并且根据这些值计算出的脂质双层的表观微粘度从1.1增加到1.8泊。此外，当从rs数据计算与脂质序参数的平方成比例的无限缓慢衰减荧光anisotropy（(r infinity)）时，这些参数也有显著增加。此外，膜的双键指数与饱和酸比例的这种降低与UDP - 葡糖醛酸基转移酶的希尔系数平行增加相关，该酶逐渐失去UDP - 葡糖醛酸的负同促效应和协同性。在所研究的21天期间，希尔系数从0.39变化到0.98。我们的观察结果一方面表明饮食中脂肪组成的变化伴随着微粒体膜脂质组成和流动性以及酶的表观协同性的改变。另一方面，它们表明UDP - 葡糖醛酸基转移酶希尔系数的评估可能用作研究肝脏微粒体膜构象变化的敏感测试。
