Certain embodiments of the invention provide a method of quantifying ubiquitin-like modification in a test protein sample comprising:
a) contacting the test protein sample with a compound of formula (I) to provide a first labeled test protein sample;
b) contacting the first labeled test protein sample with a first enzyme, wherein the first enzyme cleaves the ubiquitin-like modification from all modified amino acid residues, to provide a second labeled test protein sample;
c) contacting the second labeled test protein sample with a compound of formula (II) to provide a third labeled test protein sample; and
d) measuring the molecular weight of the protein(s) in the third labeled test protein sample to quantify the ubiquitin-like modification in the test protein sample,
wherein the compound of formula I is isotopically labeled; the compound of formula II is isotopically labeled; or the compound of formula I and the compound of formula II are differentially isotopically labeled.
本发明的某些实施例提供了一种量化测试蛋白样品中泛素样修饰的方法,包括:a)将测试蛋白样品与式(I)的化合物接触,以提供第一标记的测试蛋白样品;b)将第一标记的测试蛋白样品与第一酶接触,其中第一酶从所有修饰的
氨基酸残基中切除泛素样修饰,以提供第二标记的测试蛋白样品;c)将第二标记的测试蛋白样品与式(II)的化合物接触,以提供第三标记的测试蛋白样品;以及d)测量第三标记的测试蛋白样品中蛋白质的分子量,以量化测试蛋白样品中的泛素样修饰,其中式(I)的化合物具有同位素标记;式(II)的化合物具有同位素标记;或式(I)的化合物和式(II)的化合物具有差异同位素标记。