Updated project metadata. C13, N15 isotope labelled heavy lysine bearing the modification group, such as cr and bhb, were site-sepcifically incorporated into histone H3K56 in living cells for measurement of the modification life of H3K56cr and H3K56bhb without iinterference caused by endogenous histone modification. Utilizaing mass spectrometry, we compared with H3K56cr/bhb peptide with the H3K79 peptide as internal standard at different times. The quantitation analysis of H3K56cr and H3K56bhb at different time points can be comparative.