MEASUREMENT OF THE ISOTOPE ENRICHMENT OF STABLE ISOTOPE-LABELED PROTEINS USING

该子项目是利用NIH/NCRR资助的中心赠款提供的资源的许多研究子项目之一。子项目和研究者（PI）可能从另一个NIH来源获得主要资金，因此可以在其他CRISP条目中表示。所列机构为中心，不一定是研究者所在机构。稳定的同位素富集分子用作内标物和体内底物代谢的示踪剂。将质谱仪中测量的比率精确转换为摩尔比是复杂的，因为含有富集原子的多原子分子将导致同位素异构体的组合分布，这取决于“标记”原子的富集和数量。该效应可能潜在地导致摩尔比测量中的大误差，这取决于使用哪个同位素峰或哪些同位素峰来确定该比率。我们报告了一种计算方法，预测同位素分布在一个范围内的富集和比较预测的分布实验肽同位素分布通过傅立叶变换离子回旋共振质谱。我们的方法是准确的，在1.5%的预期同位素分布的测量富集。对于含有59、79和99原子%过量15 N的肽，该方法也具有精密度，相对标准偏差分别为4.9、2.0和0.8%。该方法是自动化的，使得在单个LC-FTICR-MS实验中可以对数千种肽进行同位素富集计算。

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Stable isotope-enriched molecules are used as internal standards and as tracers of in vivo substrate metabolism. The accurate conversion of measured ratios in the mass spectrometer to mole ratios is complicated because a polyatomic molecule containing enriched atoms will result in a combinatorial distribution of isotopomers depending on the enrichment and number of "labeled" atoms. This effect could potentially cause a large error in the mole ratio measurement depending on which isotope peak or peaks were used to determine the ratio. We report a computational method that predicts isotope distributions over a range of enrichments and compares the predicted distributions to experimental peptide isotope distributions obtained by Fourier transform ion cyclotron resonance mass spectrometry. Our approach is accurate with measured enrichments within 1.5% of expected isotope distributions. The method is also precise with 4.9, 2.0, and 0.8% relative standard deviations for peptides containing 59, 79, and 99 atom % excess 15N, respectively. The approach is automated making isotope enrichment calculations possible for thousands of peptides in a single LC-FTICR-MS experiment.