The temperature and pH dependence of conformational transitions of the chromatin subunit.
The temperature and pH dependence of conformational transitions of the chromatin subunit.
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染色质亚基构象转变的温度和 pH 依赖性。
DOI：
10.1093/nar/6.12.3845
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发表时间：
1979
影响因子：
14.9
通讯作者：
J. Horwitz
中科院分区：
文献类型：
--
作者：
V. C. Gordon;V. Schumaker;D. Olins;C. Knobler;J. Horwitz
报道了单体染色质亚基的流体力学、光谱和化学交联研究，它们是离子强度、pH和温度的函数。在早期的研究中，描述了两个依赖于盐的构象转变(Gordon等人，国家科学院学报，75,660,1978)。其中一次转变发生在0.7~2.0 mm离子强度之间，两次转变发生在5.0~11.0 mm离子强度之间。离子强度为11 mM的甲醛交联抑制了这两个转变。在本文中，我们报道了第二个转变的特征是260-320 nm区域圆二向色性光谱的变化以及流体力学性质的变化。当离子强度从5.0 mm增加到11.0 mm时，[theta]282从2000降至1500℃cm2/dmole，[theta]295从0降至-400 deg cm2/dmole。这两个转变都发生在pH 6.0~9.2的范围内。在pH为5.0时，不再观察到与离子强度相关的两个转变，圆二色谱的特征变化被抑制。在pH 5.0时，单体亚基的光谱随离子强度的变化很小，与高于pH 6.0时11 mM离子强度时的光谱相似。为了从热力学角度描述这些转变，选择了每个转变中点附近的离子强度。然后，测量S20，w和D20，w随温度的变化。通过这些数据，可以估算出转变过程中的焓和熵。
Hydrodynamic, spectroscopic, and chemical crosslinking studies on monomer chromatin subnits are reported as a function of ionic strength, pH, and temperature. In earlier studies, two salt-dependent conformational transitions were described (Gordon et al., Proceedings of the National Academy of Science, 75, 660, 1978). Transition one occurred between 0.7 and 2.0 mM ionic strength and transition two occurred between 5.0 and 11.0 mM ionic strength. Crosslinking at 11 mM ionic strength with formaldehyde suppressed both transitions. In this communication we report that the second transition was characterized by changes in the circular dichroism spectra in the 260--320 nm region as well as by changes in the hydrodynamic properties. As the ionic strength was increased from 5.0 to 11.0 mM, [theta]282 decreased from 2000 TO 1500 DEG CM2/DMOLE AND [THETA]295 decreased from 0 to -400 deg cm2/dmole. Both transitions occurred in the pH range from pH 6.0 to 9.2. At pH 5.0, the two ionic strength-dependent transitions were no longer observed and the characteristic changes in the circular dichroism spectra were suppressed. The spectra of the monomer subunits at pH 5.0 showed only small changes with ionic strength and resembled the spectra of the subunits at 11 mM ionic strength above pH 6.0. In order to characterize the transitions in thermodynamic terms an ionic strength near the midpoint of each transition was selected. Then, changes in s20,w and D20,w were measured as a function of temperature. These data allow an estimation to be made of the enthalpies and entropies of the transitions.