Biomolecular condensates perform their cellular functions via the exclusion or enrichment of molecules. Analyzing the composition of condensates is important for understanding their properties and functions. A considerable amount of work has gone into understanding the nucleic acid and protein components of condensates; however, much less is known about partitioning of small molecules and the determinants that govern their enrichment or exclusion under the conditions where they form. Now Thody et al. have measured the partitioning of approximately 1,700 biologically relevant small molecules into 4 different condensates formed through phase separation of unrelated proteins and protein–DNA mixtures.

To ensure they analyzed the partitioning of a wide range of structures, the team used a diverse library of metabolites and drugs that were not constructed using a common molecular core. Accurately measuring the partition coefficients required the team to develop two assays — one based on centrifugation followed by separation and then mass spectrometry; the other assay was based on fluorescence. These showed that partition coefficients of the small molecules varied by nearly six orders of magnitude but showed similarities between different condensates, suggesting that condensates formed from different compositions of macromolecules produce a physically similar internal environment.

生物分子凝聚物通过排除或富集分子来执行其细胞功能。分析凝聚物的成分对于了解其性质和功能非常重要。为了了解凝聚物的核酸和蛋白质成分，已经进行了大量工作;然而，关于小分子的分配以及在其形成条件下控制其富集或排斥的决定因素，人们知之甚少。现在，Thody 等人已经测量了大约 1,700 个生物相关小分子被分配成 4 种不同的缩合物，这些缩合物是通过不相关蛋白质和蛋白质-DNA 混合物的相分离形成的。

为了确保他们分析了各种结构的分配，该团队使用了不同的代谢物和药物库，这些代谢物和药物不是使用共同分子核心构建的。准确测量分配系数需要该团队开发两种检测方法——一种基于离心，然后分离，然后是质谱法;另一种测定基于荧光。这些结果表明，小分子的分配系数相差近六个数量级，但不同凝聚态之间显示出相似性，这表明由不同组成的大分子形成的凝聚态会产生物理上相似的内部环境。