Pilarska M, Wrzosek A, Pikuła S, Famulski K S
Department of Muscle Biochemistry, Nencki Institute of Experimental Biology, Warsaw, Poland.
Biochim Biophys Acta. 1991 Sep 30;1068(2):167-73. doi: 10.1016/0005-2736(91)90206-n.
Sarcolemma membrane lipid phase of skeletal muscles of hyperthyroid animals was compared to that of control (euthyroid) ones. Hyperthyroidism caused 15% decrease in cholesterol and 70% increase in the phospholipid content of the membrane. This was accompanied by the alterations in proportions between individual phospholipid classes, and was followed by changes in the composition of phospholipid fatty acids. The calculated fatty acid unsaturation index was higher for membrane lipid phase of hyperthyroid animals than of euthyroid ones. Thyroxine-induced alterations in the lipid composition of sarcolemma caused changes in the membrane fluidity and the activity of calmodulin-stimulated (Ca(2+)-Mg(2+)-ATPase. Measurements of the steady-state fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene indicated that the lipid phase transition of membrane vesicles occurred at 25.9 degrees C and at 28.9 degrees C for preparations isolated from hyperthyroid and euthyroid rabbits, respectively. Arrhenius plot break-point temperature for CaM-stimulated (Ca(2+)-Mg(2+)-ATPase activity was lower in membrane preparations isolated from hyperthyroid (26.9 degrees C) than from euthyroid ones (30.0 degrees C). Thus, the increase of the membrane fluidity presumably caused that the enzyme was characterized by the lower activation energy value. This phenomenon may be viewed as a supplementary mechanism for activation of the enzyme by thyroid hormones to previously reported elevation of the amount of (Ca(2+)-Mg(2+)-ATPase protein exerted by hyperthyroidism (Famulski et al. (1988) Eur. J. Biochem., 171, 363-368; Famulski and Wrzosek (1988) in The Ion Pumps-Structure, Function and Regulation (Stein, W.D., ed.), pp. 355-360, Alan R. Liss, New York).
将甲状腺功能亢进动物骨骼肌的肌膜脂质相与其对照（甲状腺功能正常）动物的进行了比较。甲状腺功能亢进导致膜中胆固醇含量降低15%，磷脂含量增加70%。这伴随着各个磷脂类之间比例的改变，随后是磷脂脂肪酸组成的变化。甲状腺功能亢进动物的膜脂质相计算得出的脂肪酸不饱和度指数高于甲状腺功能正常的动物。甲状腺素引起的肌膜脂质组成变化导致膜流动性和钙调蛋白刺激的（Ca(2+)-Mg(2+)-ATP酶活性发生变化。对1,6-二苯基-1,3,5-己三烯的稳态荧光偏振测量表明，从甲状腺功能亢进和甲状腺功能正常的兔子分离得到的膜囊泡的脂质相转变分别发生在25.9℃和28.9℃。从甲状腺功能亢进动物分离得到的膜制剂中，钙调蛋白刺激的（Ca(2+)-Mg(2+)-ATP酶活性的阿伦尼乌斯图断点温度（26.9℃）低于从甲状腺功能正常动物分离得到的膜制剂（30.0℃）。因此，膜流动性的增加可能导致该酶具有较低的活化能值。这种现象可被视为甲状腺激素激活该酶的一种补充机制，此前已有报道甲状腺功能亢进会使（Ca(2+)-Mg(2+)-ATP酶蛋白量增加（Famulski等人（1988年），《欧洲生物化学杂志》，171卷，363 - 368页；Famulski和Wrzosek（1988年），载于《离子泵——结构、功能与调节》（Stein，W.D.编），第355 - 360页，Alan R. Liss出版社，纽约）。
