Extended Data Fig. 1: Evidence of H3Y99 phosphopeptide presence in Yu et al. HepG2 nuclear extract, mixed and synthetic sulfopeptide samples.
From: Mass spectrometry and enzyme assays refute histone tyrosine sulfation
Extracted ion chromatograms of the tyrosine 99 phosphopeptide 3+ precursor ion (706.6709 m/z), at 6 ppm mass tolerance, in the HepG2 nuclear extract sample (a), mixed sample (b) and synthetic sulfopeptide sample (c) from Yu et al. The phosphopeptide was observed eluting at 14.09-14.18 min. in those short 30 min. gradient proteomic analysis runs. The corresponding MS1 spectrum of the H3Y99 phosphopeptide precursor, eluting at 14.09 min in the HepG2 nuclear extract sample, showed 1.56e7 abundance (inset in a) compared to an abundance of 2.56e3 at 25.45 min (d) proposed by Yu et al. MS2 spectrum supporting phosphopetide assignment was also absent around 25.45 min in Yu et al. HepG2 sample. Moreover, no evidence of phosphopeptide was observed around this retention time in both Yu et al. mixed and synthetic sulfopeptide samples.
