LAH4 is a 26-amino-acid cationic amphipathic α-helical peptide (sequence: KKALLALALHHLAHLALHLALALKKA), carrying a net charge of +5 at neutral pH thanks to 5 lysines and 4 histidines. It has a hydrophobic moment of 1.35 and average hydrophobicity of 1.28, and can bind nucleic acids spontaneously.

Its conformation changes with pH: at pH 7.5, terminal lysines anchor it across lipid bilayers as a transmembrane helix; in acidic environments, histidine imidazole groups get protonated, flipping LAH4 to lie flat on the membrane surface. Solid-state NMR confirms LAH4 preferentially binds and disturbs the acyl chains of anionic lipids (PS, PG), barely affecting neutral phosphatidylcholine (PC), and this lipid-disrupting effect intensifies under acid conditions.

The peptide’s membrane-damaging potency is controlled by the spatial angle of positively charged histidines: variants with 80° or 100° histidine angles break anionic lipid structures most effectively, while 60° and 180° variants work poorly.

Multiple modified LAH4 derivatives (LAH4-L1, LAH4-L1-R, LAH4-Leu, LAH4-L1-Leu, LAH4-L1-F) are created via amino acid substitutions. These changes adjust peptide hydrophobicity and hydrophobic moment, tuning their binding to nucleic acids and cell membranes, and all LAH4-type peptides break endosomal membranes in a pH-responsive way to deliver nucleic acids into cells.

• Mason AJ, Martinez A, Glaubitz C, Danos O, Kichler A, Bechinger B. The antibiotic and DNA-transfecting peptide LAH4 selectively associates with, and disorders, anionic lipids in mixed membranes. FASEB J. 2006 Feb;20(2):320-2. doi: 10.1096/fj.05-4293fje. Epub 2005 Dec 13. PMID: 16352649.
• Langlet-Bertin B, Leborgne C, Scherman D, Bechinger B, Mason AJ, Kichler A. Design and evaluation of histidine-rich amphipathic peptides for siRNA delivery. Pharm Res. 2010 Jul;27(7):1426-36. doi: 10.1007/s11095-010-0138-2. PMID: 20393870.

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。