Effect of post-translational modifications status on H3 turnover. Mass spectrometry (MS) spectrum of the H3 9-17 peptide (left) unmodified and (right) monomethylated on K9 collected from cells before and 1 day after the labeling time course. Contour plots below the H3K9un and H3K9me1 MS spectra are shown for the optimization of the turnover parameter (k-1) versus the addition of two labeled lysines (k2), where the contours represent values (color bar) of the objective/error function of the model in explaining the variability of the data. The boundaries of the contours equal z(k) × (1+3/11 × F0.05(3,11)), where z(k) is the global minimum of the calculated objective value for the H3K9un and H3K9me1 optimization. Note the lack of overlap of the two contours.