Quantitative peptidomics and proteomics often use chemical tags to covalently modify peptides with reagents that differ in the number of stable isotopes, allowing for quantitation of the relative peptide levels in the original sample based on the peak height of each isotopic form. Different chemical reagents have been used as tags for quantitative peptidomics and proteomics, and all have strengths and weaknesses. One of the simplest approaches uses formaldehyde and sodium cyanoborohydride to methylate amines, converting primary and secondary amines into tertiary amines. Up to five different isotopic forms can be generated, depending on the isotopic forms of formaldehyde and cyanoborohydride reagents, allowing for five-plex quantitation. However, the mass difference between each of these forms is only 1 Da per methyl group incorporated into the peptide, and for many peptides there is substantial overlap from the natural abundance of ¹³C and other isotopes. In this study, we calculated the contribution from the natural isotopes for 26 native peptides and derived equations to correct the peak intensities. These equations were applied to data from a study using human embryonic kidney HEK293T cells in which five replicates were treated with 100 nM vinblastine for 3 h and compared with five replicates of cells treated with control medium. The correction equations brought the replicates to the expected 1:1 ratios and revealed significant decreases in levels of 21 peptides upon vinblastine treatment. These equations enable accurate quantitation of small changes in peptide levels using the reductive methylation labeling approach.

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定量肽组学和蛋白质组学经常使用化学标签通过稳定同位素数目不同的试剂对肽进行共价修饰，从而可以根据每种同位素形式的峰高对原始样品中的相对肽水平进行定量。不同的化学试剂已被用作定量肽组学和蛋白质组学的标签，并且各有优缺点。最简单的方法之一是使用甲醛和氰基硼氢化钠将胺甲基化，将伯胺和仲胺转化为叔胺。根据甲醛和氰基硼氢化物试剂的同位素形式，最多可以生成五种不同的同位素形式，从而可以进行五重定量。然而，¹³ C和其他同位素。在这项研究中，我们计算了天然同位素对26种天然肽的贡献，并推导了方程以校正峰强度。将这些方程式应用于使用人类胚胎肾脏HEK293T细胞进行的研究数据，其中将五个重复样本用100 nM长春花碱处理3 h​​，然后与使用对照培养基处理的五个重复样本进行比较。校正方程式使复制品达到预期的1：1比例，并显示了长春碱处理后21种肽水平的显着降低。这些方程式可使用还原甲基化标记方法准确定量肽水平的微小变化。

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