Determination of isotopic labeling of proteins by precursor ion scanning liquid chromatography/tandem mass spectrometry of derivatized amino acids applied to nuclear magnetic resonance studies
A method has been developed for the quantitation of isotopic labeling of proteins using liquid chromatography/tandemmassspectrometry (LC/MS/MS) for the application of protein nuclear magnetic resonance (NMR) studies. NMR relies on specific isotopic nuclei, such as 13C and 15N, for detection and, therefore, isotopic labeling is an important sample preparation step prior to in‐depth structural characterization
已经开发出一种使用液相色谱/串联质谱法(LC / MS / MS)定量蛋白质同位素标记的方法,用于蛋白质核磁共振(NMR)研究。NMR依靠特定的同位素核(例如13 C和15 N)进行检测,因此,同位素标记是蛋白质深入结构表征之前的重要样品制备步骤。这项研究的目的是开发一种鲁棒的定量测定方法,以评估蛋白质中的同位素标记,同时保留有关单个氨基酸标记程度的信息。
Measurement of 15N enrichment of glutamine and urea cycle amino acids derivatized with 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate using liquid chromatography–tandem quadrupole mass spectrometry
6-Aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC) is an amino acid-specific derivatizing reagent that has been used for sensitive amino acid quantification by liquid chromatography-tandem quadrupole mass spectrometry (LC-MS/MS). In this study, we aimed to evaluate the ability of this method to measure the isotopic enrichment of amino acids and to determine the positional N-15 enrichment of urea cycle amino acids (i.e., arginine, omithine, and citrulline) and glutamine. The distribution of the M and M + 1 isotopomers of each natural AQC-amino acid was nearly identical to the theoretical distribution. The standard deviation of the (M + 1)/M ratio for each amino acid in repeated measurements was approximately 0.1%, and the ratios were stable regardless of the injected amounts. Linearity in the measurements of N-15 enrichment was confirmed by measuring a series of N-15-labeled arginine standards. The positional N-15 enrichment of urea cycle amino acids and glutamine was estimated from the isotopic distribution of unique fragment ions generated at different collision energies. This method was able to identify their positional N-15 enrichment in the plasma of rats fed 15N-labeled glutamine. These results suggest the utility of LC-MS/MS detection of AQC-amino acids for the measurement of isotopic enrichment in N-15-labeled amino acids and indicate that this method is useful for the study of nitrogen metabolism in living organisms. (C) 2015 Elsevier Inc. All rights reserved.