The K8 peptide, an octalysine-modified cell-penetrating peptide, is a cationic peptide composed of eight lysine residues. It is structurally analogous to the octaarginine (R8) peptide but differs in its amino acid composition, replacing arginine with lysine. Studies comparing K8-modified liposomes (K8-Lip) with R8-modified liposomes (R8-Lip) have shown that K8-Lip exhibits similar physical properties, such as size and ζ-potential, but demonstrates significantly lower efficiency in promoting cross-presentation of antigen peptides. Unlike R8-Lip, K8-Lip does not enhance the C-terminal trimming of antigen-derived peptides, a critical step in generating mature MHC-I peptides. This functional disparity highlights the unique role of arginine-rich peptides in antigen processing.

Further investigations reveal that K8-Lip and R8-Lip share comparable cellular uptake mechanisms, primarily through macropinocytosis, and exhibit similar endosomal escape efficiencies in dendritic cells. However, K8-Lip fails to enhance proteasome-dependent C-terminal trimming of extended antigen peptides, such as SIINFEKLTEWTS, which is essential for efficient MHC-I presentation. These findings suggest that the lysine-rich structure of K8, unlike the arginine-rich R8, lacks the capacity to modulate proteasomal activity or downstream peptide processing, underscoring the specificity of arginine residues in optimizing antigen presentation pathways.

• Nakamura, T., Ono, K., Suzuki, Y., Moriguchi, R., Kogure, K., & Harashima, H. (2014). Octaarginine-modified liposomes enhance cross-presentation by promoting the C-terminal trimming of antigen peptide. Molecular pharmaceutics, 11(8), 2787–2795. https://doi.org/10.1021/mp500147y

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。