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DSC study of cold and heat denaturation of β-lactoglobulin A with urea

机译：DSC研究尿素对β-乳球蛋白A的冷热变性

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IN the field of thermodynamics of protein solutions, there are two kinds of denaturation induced by temperature changes. One of them is the commonest heat denaturation induced by temperature increasing and accompanied by a heat absorption and an increase of enthalpy and entropy. The other is cold denaturation, predicted by Brandts over thirty years ago: the compact ordered structure of protein molecules in the native state is induced into a disordered structure with temperature decreasing. The progress of cold denaturation is accompanied by a heat release and a decrease of enthalpy and entropy. The transformation from an ordered structure to a disordered structure will result in an increase of randomness; however, the entropy is not increased but decreased. All these make the cold denaturation seemingly nonun-derstandable. This thermodynamic paradox has aroused great interest among scientists. Different from spectroscopy such as NMR, UV and CD, calorimetry may directly and independently of model determine the denaturational enthalpy. Therefore a strong desire has long been cherished that the exothermic denaturation at low temperature may directly be observed with calorimetry. However, up to now, only for a few proteins has this long cherished desire been fulfilled. In literature the concentration of protein studied was less than 1 % ; the lowest temperature reached by cooling was -- 8°C, and in some cases the peak of cold denaturation recorded was incomplete. In comparison with heat denaturation, the knowledge of cold denaturation is too little. To further the knowledge about the cold denaturation, researchers have been making efforts to make the cold denaturation directly observable for more proteins and under more various conditions. The purpose of this work is to observe directly the behaviour of β-lactoglobulin A (β-LgA) during cold and heat denaturation with differential scanning calorimetry (DSC).
机译：在蛋白质溶液的热力学领域，温度变化引起两种变性。其中之一是由温度升高引起的最常见的热变性，并伴随着吸热以及焓和熵的增加。另一个是冷变性，这是Brandts在30年前预测的：随着温度的降低，天然状态的蛋白质分子的紧凑有序结构被诱导为无序结构。冷变性的进展伴随着热量的释放以及焓和熵的降低。从有序结构到无序结构的转换将导致随机性的增加;但是，熵并没有增加而是减少了。所有这些使得冷变性似乎不可理解。这种热力学悖论引起了科学家的极大兴趣。不同于NMR，UV和CD等光谱学，量热法可以直接且独立于模型确定变性焓。因此，长期以来强烈希望可以通过量热法直接观察到低温下的放热变性。然而，直到现在，只有少数蛋白质才满足了这种长期以来的珍贵愿望。在文献中研究的蛋白质浓度小于1％;冷却达到的最低温度为-8°C，在某些情况下记录的冷变性峰不完整。与热变性相比，冷变性的知识太少。为了进一步了解冷变性，研究人员一直在努力使冷变性直接可用于更多蛋白质和更多不同条件下观察到。这项工作的目的是通过差示扫描量热法（DSC）直接观察冷变性和热变性过程中β-乳球蛋白A（β-LgA）的行为。

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