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An Improved Measurement of Isotopic Ratios by High Resolution Mass Spectrometry |
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| Authors: | Serguei Ilchenko Stephen F. Previs Nadia Rachdaoui Belinda Willard Arthur J. McCullough Takhar Kasumov | |
| Affiliation: | 1. Center for Proteomics and Bioinformatics, Case Western Reserve University, Cleveland, OH, 44106, USA 2. Department of Nutrition, School of Medicine, Case Western Reserve University, Cleveland, OH, 44106, USA 6. Pharmacokinetics, Pharmacodynamics, and Drug Metabolism, Merck, 126 E. Lincoln Ave., Rahway, NJ, 07065, USA 3. Department of Medicine, School of Medicine, Case Western Reserve University, Cleveland, OH, 44106, USA 4. Department of Research Core Services, Cleveland Clinic, Cleveland, OH, 44195, USA 5. Department of Gastroenterology and Hepatology, Cleveland Clinic, Cleveland, OH, 44195, USA |
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| Abstract: | The study of protein kinetics requires an accurate measurement of isotopic ratios of peptides. Although Fourier transform-ion cyclotron resonance (FT-ICR) mass spectrometers yield accurate mass measurements of analytes, the isotopologue ratios are consistently lower than predicted. Recently, we demonstrated that the magnitude of the spectral error in the FT-ICR mass spectrometer is proportional to the scan duration of ions. Here, we present a novel isotopic ratio extrapolation (IRE) method for obtaining accurate isotopic ratio measurements. Accuracy is achieved by performing scans with different duration and extrapolation of the data to the initial moment of the ion rotation; IRE minimizes the absolute isotopic ratio error to ≤1 %. We demonstrate the application of IRE in protein turnover studies using 2H2O-metabolic labeling. Overall, this technique allows accurate measurements of the isotopic ratios of proteolytic peptides, a critical step for enabling routine studies of proteome dynamics.  | |
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