Buchet R, Jona I, Martonosi A
Department of Biochemistry and Molecular Biology, State University of New York, Syracuse 13210.
Biochim Biophys Acta. 1989 Aug 7;983(2):167-78. doi: 10.1016/0005-2736(89)90230-7.
The effect of dimethyl sulfoxide (DMSO) on the structure of sarcoplasmic reticulum was analyzed by Fourier transform infrared (FTIR) and fluorescence spectroscopy. Exposure of sarcoplasmic reticulum vesicles to 35% DMSO (v/v) at 2 degrees C for several hours in a D2O medium produced no significant change in the phospholipid and protein Amide I regions of the FTIR spectra, but the intensity of the Amide II band decreased, presumably due to proton/deuterium exchange. At 40% to 60% DMSO concentration a shoulder appeared in the FTIR spectra at 1630 cm-1, that is attributed to the formation of new beta or random coil structures; irreversible loss of ATPase activity accompanied this change. At 70% DMSO concentration the intensity of the main Amide I band at 1639 cm-1 decreased and a new band appeared at 1622 cm-1, together with a shoulder at 1682 cm-1. These changes indicate an abrupt shift in the conformational equilibrium of Ca2+-ATPase from alpha to beta structure or to a new structure characterized by weaker hydrogen bonding. Decrease of ionization of aspartate and glutamate carboxyl groups in the presence of DMSO may also contribute to the change in intensity at 1622 cm-1. The changes were partially reversed upon removal of DMSO. Exposure of sarcoplasmic reticulum vesicles to 1.5 kbar pressure for 1 h at 2 degrees C in an EGTA-containing (low Ca2+) medium causes irreversible loss of ATPase activity, with the appearance of new beta structure, and abolition of the Ca2+-induced fluorescence response of FITC covalently bound to the Ca2+-ATPase; DMSO (35%) stabilized the Ca2+-ATPase against pressure-induced changes in structure and enzymatic activity, while urea (0.8 M) had the opposite effect.
通过傅里叶变换红外光谱（FTIR）和荧光光谱分析了二甲基亚砜（DMSO）对肌浆网结构的影响。在重水（D2O）介质中，于2℃将肌浆网囊泡暴露于35%（v/v）的DMSO中数小时，FTIR光谱的磷脂和蛋白质酰胺I区域未发生显著变化，但酰胺II带的强度降低，这可能是由于质子/氘交换所致。当DMSO浓度为40%至60%时，FTIR光谱在1630 cm-1处出现一个肩峰，这归因于新的β结构或无规卷曲结构的形成；伴随这一变化的是ATP酶活性的不可逆丧失。当DMSO浓度为70%时，1639 cm-1处的主要酰胺I带强度降低，1622 cm-1处出现一个新带，同时在1682 cm-1处有一个肩峰。这些变化表明Ca2+-ATP酶的构象平衡从α结构突然转变为β结构或转变为以较弱氢键为特征的新结构。在DMSO存在下，天冬氨酸和谷氨酸羧基的电离减少也可能导致1622 cm-1处强度的变化。去除DMSO后，这些变化部分逆转。在含乙二醇双四乙酸（EGTA）（低Ca2+）的介质中，于2℃将肌浆网囊泡暴露于1.5千巴压力下1小时，会导致ATP酶活性不可逆丧失，出现新的β结构，并消除与Ca2+-ATP酶共价结合的异硫氰酸荧光素（FITC）的Ca2+诱导荧光响应；35%的DMSO可稳定Ca2+-ATP酶，使其免受压力诱导的结构和酶活性变化的影响，而0.8 M的尿素则具有相反的作用。
