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. Author manuscript; available in PMC: 2012 Nov 1.
Published in final edited form as: Toxicol Appl Pharmacol. 2011 Jun 24;256(3):337–347. doi: 10.1016/j.taap.2011.06.016

Figure 4.

Figure 4

Limit of detection of phosphorylated butyrylcholinesterase. Partially purified butyrylcholinesterase was digested with pepsin and mixed in known ratios with 100%-labeled CBDP-butyrylcholinesterase that also had been digested with pepsin. The phosphorylated peptides were purified on titanium oxide, eluted with ammonium hydroxide, reduced in volume, and spotted on a MALDI plate with DHB matrix. MS spectra were acquired in negative mode at 5000 volts. Spectra represent phosphorylated peptide from 12 units of butyrylcholinesterase (16.6 micrograms) containing 0.05 to 1% CBDP-treated butyrylcholinesterase. As little as 0.05% phosphorylated butyrylcholinesterase is detectable as a peptide of mass 874.2 Da, in negative mode.