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. Author manuscript; available in PMC: 2017 Dec 27.
Published in final edited form as: ACS Chem Biol. 2016 Sep 28;11(11):2981–2990. doi: 10.1021/acschembio.6b00507

Figure 2.

Figure 2

Labeling method and confirmation of heavy isotope incorporation. (A) We fed heavy bacteria grown on 15N to T. thermophila. We then purified endogenous T. thermophila tubulin; our protocol resulted in full incorporation of 15N into tubulin. (B) Mass spectrometry showing two degrees of incorporation of 15N into the tubulin peptide (INVYYNEATGGR). The highest green peak appears at the m/z position expected for the fully 14N, 12C peptide. The cluster of three peaks result from the incorporation of single heavy atoms, primarily 13C carbon, which has a natural abundance of 1.1%. In blue are the fully 15N labeled peptides, with a similar peptide distribution to the natural abundance peptides, but at a mass increased by the number of nitrogen atoms in the peptide.