Kharakoz D P, Bychkova V E
Institute of Theoretical and Experimental Biophysics, Russian Academy of Science, Moscow Region.
Biochemistry. 1997 Feb 18;36(7):1882-90. doi: 10.1021/bi960264r.
Specific partial volume, partial compressibility, and sound absorption changes induced by the native-to-molten globule state (acid) transition of the human alpha-lactalbumin were measured by means of densitometric and ultrasonic techniques and interpreted in terms of the protein molecule phase transition and interphase water transfer. The molten globule is a highly hydrated state containing about 270 water molecules inside. Intrinsic mass density of the hydrated (swollen) interior of the protein molecule is 5% smaller and the intrinsic compressibility coefficient 2 times higher than those in the native molecule. The obtained intrinsic compressibility falls into the range of values characteristic of highly associated liquids. Water inside the molten globule interior occupies less volume and is less compressible than in solvent phase. The acoustic relaxation was found to increase indicating an appearance of pressure-dependent processes. The commonly used approach to the calculation of the volume fluctuations of protein molecules, based on the well-known relation between the volume fluctuations and compressibility, is of limited applicability to the highly hydrated molten globule state because a large, if not predominant, part of the fluctuations may be determined by the process of water exchange between the molten globule and bulk solvent.
通过密度测量和超声技术，测量了人α-乳白蛋白从天然态到熔球态（酸性）转变所引起的特定部分体积、部分压缩性和声吸收变化，并根据蛋白质分子的相变和相间水转移进行了解释。熔球态是一种高度水合的状态，内部含有约270个水分子。蛋白质分子水合（肿胀）内部的固有质量密度比天然分子小5%，固有压缩系数比天然分子高2倍。所获得的固有压缩性落入高度缔合液体的特征值范围内。熔球态内部的水比溶剂相中的水占据的体积更小且更不易压缩。发现声弛豫增加，表明出现了压力依赖性过程。基于体积涨落与压缩性之间的著名关系来计算蛋白质分子体积涨落的常用方法，对于高度水合的熔球态适用性有限，因为很大一部分（如果不是主要部分）涨落可能由熔球态与大量溶剂之间的水交换过程决定。
