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Intramolecular distribution of 13C/12C isotopes in amino acids of diverse origins.
Amino Acids ( IF 3.5 ) Pub Date : 2020-06-27 , DOI: 10.1007/s00726-020-02863-y
Cornelia Rasmussen 1, 2 , David W Hoffman 2, 3
Affiliation  

Carbon stable isotope analysis can provide information about the origin and synthetic pathways that produce organic molecules, with applications in chemical, medical and (bio)geochemical sciences. The 13C/12C isotope ratios of organics such as amino acids are most commonly obtained as whole molecule averages. In this study, we apply proton nuclear magnetic resonance spectroscopy to conduct position-specific carbon isotope analyses of l-/d-alanine, l-threonine and l-histidine from different sources, in addition to molecule average stable isotope analyses obtained via mass spectrometry. Our results demonstrate that carbon isotope ratios can vary significantly between the individual carbon positions within an amino acid. For example, the β- and γ- carbons of l-threonine can differ in 13C/12C ratio by > 20 ‰. Comparisons of the position-specific and whole molecule average stable isotope abundances show that whole molecule analyses can mask the intramolecular isotope variation. These results provide the first experimentally measured position-specific isotope ratios for alpha and side chain carbons of alanine, threonine and histidine. Comparison with previous ab initio calculations of intramolecular equilibrium fractionation shows that the carbon isotope distributions are not at equilibrium, thus kinetic isotope effects play a significant role in amino acid synthesis. We hypothesize that position-specific 13C/12C isotope ratios provide an “isotopic fingerprint” that can give insight into the origin or synthesis pathway that formed an amino acid, and that this emerging analytical field will be a valuable addition to traditional stable isotope analysis.

中文翻译:

不同来源氨基酸中13C / 12C同位素的分子内分布。

碳稳定同位素分析可提供有关产生有机分子的起源和合成途径的信息,并应用于化学,医学和(生物)地球化学科学中。最常见的有机物(例如氨基酸)的13 C / 12 C同位素比率是整个分子的平均值。在这项研究中,我们应用质子核磁共振波谱对l- / d-丙氨酸,l-苏氨酸和l-进行特定位置的碳同位素分析除了通过质谱获得的分子平均稳定同位素分析外,还包括来自不同来源的β-组氨酸。我们的结果表明,氨基酸中各个碳原子之间的碳同位素比可能有很大差异。例如,β-和γ-碳-苏氨酸可在不同13 C / 12C比> 20‰。位置特异性和全分子平均稳定同位素丰度的比较表明,全分子分析可以掩盖分子内同位素的变化。这些结果为丙氨酸,苏氨酸和组氨酸的α和侧链碳提供了第一个实验测量的位置特异性同位素比。与先前分子内平衡分级分离的从头算的比较表明,碳同位素分布不处于平衡状态,因此动力学同位素效应在氨基酸合成中起着重要作用。我们假设特定位置的13 C / 12C同位素比率提供了一个“同位素指纹”,可以洞悉形成氨基酸的起源或合成途径,并且这种新兴的分析领域将为传统的稳定同位素分析提供有价值的补充。
更新日期:2020-06-27
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