Saponins are a diverse group of secondary plant metabolites, some of which display hemolytic toxicity due to plasma membrane permeabilization. This feature is employed in biological applications for transferring hydrophilic molecules through cell membranes. Widely used commercial saponins include digitonin and saponins from soap tree bark, both of which constitute complex mixtures of little definition. We assessed the permeabilization power of pure saponins towards cellular membranes in an effort to detect novel properties and to improve existing applications.

In a respirometric assay, we characterized half-maximal permeabilization of the plasma membrane for different metabolites, of the mitochondrial outer membrane for cytochrome C and the full solubilization of mitochondrial inner membrane protein complexes.

Beyond the complete list as repository for the field, we highlight several findings with direct applicability. First, we identified and validated α-chaconine as alternative permeabilization agent in respirometric assays of cultured cells and isolated synaptosomes, superior to digitonin in its tolerability for mitochondria. Second, we identified glycyrrhizic acid to form exceptionally small pores impermeable for adenosine diphosphate. Third, in a concentration dependent manner, tomatine proved to be able to selectively permeabilize the mitochondrial outer, but not inner membrane, allowing for novel states in which to determine cytochrome C oxidase activity.

In summary, we provide a list of the permeabilization properties of 18 pure saponins. The identification of two saponins, namely tomatine and chaconine, with direct usability in improved or novel cell biological applications within this small subgroup demonstrates the tremendous potential for further functional screening of pure saponins.

皂苷是植物次生代谢产物的不同种类，其中一些由于质膜透化而显示出溶血毒性。此功能在生物学应用中用于通过细胞膜转移亲水分子。广泛使用的市售皂苷包括洋地黄皂苷和肥皂树皮中的皂苷，两者均构成定义不清的复杂混合物。我们评估了纯皂苷对细胞膜的通透能力，以发现新特性并改善现有应用。

在呼吸测定中，我们表征了质膜对不同代谢物的半数最大通透性，线粒体外膜对细胞色素C的半透性和线粒体内膜蛋白复合物的完全溶解。

除了作为该领域的存储库的完整列表之外，我们重点介绍了一些具有直接适用性的发现。首先，我们在培养细胞和分离的突触小体的呼吸测定中鉴定并验证了α-查茄碱作为替代的通透剂，其对线粒体的耐受性优于洋地黄皂苷。其次，我们确定甘草酸形成了二磷酸腺苷不可渗透的特别小的孔。第三，以浓度依赖性的方式，番茄素被证明能够选择性地渗透线粒体的外膜，而不是内膜，从而可以确定细胞色素C氧化酶活性的新状态。

总之，我们提供了18种纯皂苷的通透性列表。鉴定两个皂苷，即番茄碱和查茄碱，可直接用于该小亚组中改良的或新颖的细胞生物学应用中，这表明了进一步功能筛选纯皂苷的巨大潜力。