The present invention provides methods for analyzing a peptide or peptides of interest in a protein sample using a combination of a relatively generic isotope tag with a decoupled selection process, allowing simplified customization of the application with a single reagent. These methods comprise providing a first and a second protein sample; labeling the first protein sample with a first Universal Peptide Isotope Tag (U-PIT) reagent and the second protein sample with a second U-PIT reagent; separating the peptide of interest from the combined first and second protein samples; and determining the relative amount of the first U-PIT reagent and the second U-PIT reagent bound to the peptide or peptides of interest. The U-PIT label of the present inventive methods has the following general formula
A-B-C
wherein A is a nucleophilic reactive group, B is a detectable moiety that can be isotopically labeled, and C is a charge replacement group.
本发明提供了一种使用相对通用的同位素标记结合解耦合的选择过程来分析蛋白质样品中感兴趣的肽段的方法,允许使用单一试剂简化应用定制。这些方法包括提供第一和第二蛋白质样品;用第一通用肽同位素标记(U-
PIT)试剂标记第一蛋白质样品,用第二U-
PIT试剂标记第二蛋白质样品;从组合的第一和第二蛋白质样品中分离出感兴趣的肽段;并确定第一U-
PIT试剂和第二U-
PIT试剂与感兴趣的肽段或肽段结合的相对量。本发明中的U-
PIT标签具有以下通用公式A-B-C,其中A是亲核反应基团,B是可同位素标记的可检测基团,C是电荷替代基团。