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. Author manuscript; available in PMC: 2014 May 30.
Published in final edited form as: Anal Chem. 2012 Sep 11;84(19):8340–8344. doi: 10.1021/ac3018873

Figure 2.

Figure 2

Characterization of the 15N-apoE4 standard. (A) Experimental mass spectrum of a representative peptide (15N-AATVGSLAGQPLQER) from 15N-apoE4. The labeling incorporation was determined to be 99% by comparison to the simulated spectrum. (B) Calibration curves for quantification of total apoE (ELQAAQAR peptide) and specific apoE4 (LGADMEDVR peptide) in the temporal cortex homogenate. The area ratio of a corresponding heavy peptide to light peptide was plotted versus the amount of 15N-apoE4 supplemented. The data for three transitions per peptide were combined and are presented as the mean.