Ranatuerins are a family of antimicrobial peptides isolated from the skin of the American bullfrog, Rana catesbeiana. Nine peptides, designated ranatuerins 1 through 9, were purified from an extract of adult bullfrog skin and characterized. These peptides are structurally diverse: ranatuerins 1 and 4 contain an intramolecular disulfide bridge that forms a heptapeptide ring, while ranatuerins 2 and 3 feature a disulfide bridge forming a hexapeptide ring. Ranatuerins 5 through 9 are shorter peptides comprising 12 to 14 amino acids and show sequence similarity to the hemolytic peptides A1 and B9 previously isolated from the skin of Rana esculenta.

Ranatuerrin 1 (sequence: SMLSVLKNLGKVGLGFVACKINKQC) exhibits the broadest spectrum of antimicrobial activity among the peptides, inhibiting the growth of Staphylococcus aureus, Escherichia coli, and the yeast Candida albicans. Structural analysis predicts that ranatuerins 2, 3, and 4 contain a single amphipathic alpha-helix, while ranatuerin 1 possesses two alpha-helical regions joined by a glycine-containing hinge, a conformation resembling that of cecropin-family antimicrobial peptides. Ranatuerins 5 through 8 are predicted to contain a single alpha-helical region, whereas ranatuerin 9 is predicted to adopt either a random coil or a beta-sheet structure.

• Goraya J, Knoop FC, Conlon JM. Ranatuerins: antimicrobial peptides isolated from the skin of the American bullfrog, Rana catesbeiana. Biochem Biophys Res Commun. 1998;250(3):589-92.
• Mechkarska M, Ojo OO, Meetani MA, Coquet L, Jouenne T, Abdel-Wahab YH, Flatt PR, King JD, Conlon JM. Peptidomic analysis of skin secretions from the bullfrog Lithobates catesbeianus (Ranidae) identifies multiple peptides with potent insulin-releasing activity. Peptides. 2011 Feb;32(2):203-8.

三氟乙酸（Trifluoroacetic acid，简称 TFA）是高效液相色谱（简称 HPLC）纯化过程中常用的反离子。TFA 的存在可能会对肽的净重量、外观及溶解度产生影响，具体如下：

对净重量的影响：TFA 盐会增加产物的总质量。在大多数情况下，肽的含量占总重量的 80% 以上，剩余部分则为 TFA。

对溶解度的影响：TFA 盐通常能提高肽在水溶液中的溶解度。

在生物检测中的影响：对于大多数标准的体外检测，残留的 TFA 水平一般不会造成干扰。但需注意，在高灵敏度的细胞研究或生化研究中，需关注其存在可能带来的影响。

干品多肽的重量中不仅仅包含多肽，还包含有一些非肽的组份，如水、被吸收的溶剂、配位离子和盐等。肽的净含量是指肽在其中的重量百分比，这个百分比的数值范围很大，可能从50%到90%，取决于纯度、序列以及合成和纯化的方法，不要将肽的净含量和肽的纯度混为一谈，他们是两个完全不同的概念。纯度通常是通过HPLC测定的。纯度定义的是多肽样品中含正确序列的组分的百分比，而肽的净含量是指样品中肽类物质相对于总物质所占的百分比，肽的净含量通常是氨基酸组分分析或紫外分光法测定的，这个信息主要是在一些对肽的浓度很敏感的实验中，对计算肽的浓度是很重要的。