Gliko Olga, Pan Weichun, Katsonis Panagiotis, Neumaier Nikolaus, Galkin Oleg, Weinkauf Sevil, Vekilov Peter G
Department of Chemical and Biomolecular Engineering, University of Houston, Houston, TX 77204, USA.
J Phys Chem B. 2007 Mar 29;111(12):3106-14. doi: 10.1021/jp068827o. Epub 2007 Mar 8.
Dense liquid phases, metastable with respect to a solid phase, but stable with respect to the solution, have been known to form in solutions of proteins and small-molecule substances. Here, with the protein lumazine synthase as a test system, using dynamic and static light scattering and atomic force microscopy, we demonstrate submicron size clusters of dense liquid. In contrast to the macroscopic dense liquid, these clusters are metastable not only with respect to the crystals, but also with respect to the low-concentration solution: the characteristic cluster lifetime is limited to approximately 10 s, after which they decay. The cluster population is detectable only if they occupy >10(-6) of the solution volume and have a number density >105 cm-3 for 3 to 11% of the monitored time. The cluster volume fraction varies within wide limits and reaches up to 10(-3). Increasing protein concentration increases the frequency of cluster detection but does not affect the ranges of the cluster sizes, suggesting that a preferred cluster size exists. A simple Monte Carlo model with protein-like potentials reproduces the metastable clusters of dense liquid with limited lifetimes and variable sizes and suggests that the mean cluster size is determined by the kinetics of growth and decay and not by thermodynamics.
在蛋白质和小分子物质的溶液中，已知会形成相对于固相呈亚稳态但相对于溶液稳定的致密液相。在此，以蛋白质鲁美嗪合酶作为测试系统，利用动态和静态光散射以及原子力显微镜，我们展示了亚微米尺寸的致密液滴簇。与宏观致密液相不同，这些簇不仅相对于晶体呈亚稳态，而且相对于低浓度溶液也呈亚稳态：特征性的簇寿命限制在大约10秒，之后它们就会衰变。只有当簇占据溶液体积的>10(-6)且在监测时间的3%至11%内数密度>105 cm-3时，才能检测到簇的数量。簇的体积分数在很宽的范围内变化，最高可达10(-3)。增加蛋白质浓度会增加检测到簇的频率，但不影响簇尺寸的范围，这表明存在一个优选的簇尺寸。一个具有类似蛋白质势的简单蒙特卡罗模型再现了具有有限寿命和可变尺寸的致密液的亚稳态簇，并表明平均簇尺寸由生长和衰变动力学而非热力学决定。
