Natural intramolecular isotope measurements in physiology: elements of the case for an effort toward high-precision position-specific isotope analysis.
Natural intramolecular isotope measurements in physiology: elements of the case for an effort toward high-precision position-specific isotope analysis.
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DOI：
10.1002/rcm.325
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发表时间：
2001-08
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影响因子：
--
通讯作者：
J. Brenna
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文献类型：
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作者：
J. Brenna
生物体中可获得的化学信息可分为三个主要领域：大分子、小分子和同位素比率。有关生理状态的信息通常通过在大分子和小分子领域进行定性和定量分析来获得。基因组学和蛋白质组学是分析大分子的新兴方法，这两个领域都产生了关于当前生理状态的明确信息。在这些领域中，关于个体过去的生理状态的记录相对较少。自然的同位素可变性，特别是在分子内水平上，可能会保留更多的生理历史。由于普遍存在的同位素分馏，每个分子中每个立体化学独特的位置都有一个反映合成和降解过程的同位素比率。这一事实突显了大量基本上未被研究的有机化学信息。同位素测量可以根据分析物的化学复杂性分为散装的、化合物特定的、位置特定的或分子内的。同位素比率分析的最新进展正在改变自然科学，特别是使用整体方法回答有关生态系统的问题；然而，它们对生理学的影响相对较小。这可能是因为极其复杂的生理问题要求在特定位置的同位素分析(PSIA)中提供非常有选择性的信息。基于同位素比值质谱仪(IRMS)的相对较少的高精度PSIA研究揭示了关键生理化合物包括氨基酸、葡萄糖、甘油、醋酸酯、脂肪酸和嘌呤的分子内同位素比值差异。这些分析中的大多数都是通过费力的离线方法完成的；然而，最近仪器的进步预示着快速的PSIA将是解决真正的生理问题所必需的。气相裂解已被证明是高精度测定分子碎片~(13)C/~(12)C的有效方法，并正在出现将基于C的PSIA扩展到N和其他有机元素的技术。有两个相关的努力是有必要的，(A)开发快速、方便和灵敏的高精度PSIA方法，这是(B)对代谢状态与分子内同位素比率的关系进行协调研究的必要先导。后一个目标所固有的是，需要识别长寿细胞中的长寿分子，这些分子保留了早期同位素条件的记录，就像对死后的人类神经元DNA所显示的那样。利用分子内位置之间已知的代谢前体-产物关系，未来生理同位素分馏的研究应该会揭示饮食和环境与观测到的同位素比率的关系。这门同位素生理学，或简称同位素生理学，应该为阐明影响后来健康的早期因素增加一个重要工具，这可能是生物医学问题中最困难的一类。
Chemical information available in organisms can be categorized into three major domains, macromolecular, small molecules, and isotope ratios. Information about physiological state is commonly obtained by qualitative and quantitative analysis in the macromolecular and small molecule domains. Genomics and proteomics are emerging approaches to analysis of macromolecules, and both areas yield definitive information on present physiological state. There is relatively little record of past physiological states of the individual available in these domains. Natural isotopic variability, particularly on an intramolecular level, is likely to retain more physiological history. Because of ubiquitous isotopic fractionation, every stereochemically unique position in every molecule has an isotope ratio that reflects the processes of synthesis and degradation. This fact highlights a vast amount of organismal chemical information that is essentially unstudied. Isotope measurements can be classified according to the chemical complexity of the analyte into bulk, compound-specific, and position-specific or intramolecular levels. Recent advances in analysis of isotope ratios are transforming natural science, and particularly answering questions about ecosystems using bulk methods; however, they have had relatively little impact on physiology. This may be because the vast complexities of physiological questions demand very selective information available in position-specific isotope analysis (PSIA). The relatively few high-precision PSIA studies, based on isotope ratio mass spectrometry (IRMS), have revealed intramolecular isotope ratio differences in pivotal physiological compounds including amino acids, glucose, glycerol, acetate, fatty acids, and purines. The majority of these analyses have been accomplished by laborious offline methods; however, recent advances in instrumentation presage rapid PSIA that will be necessary to attack real physiological problems. Gas-phase pyrolysis has been shown to be an effective method to determine (13)C/(12)C at high precision for molecular fragments, and technologies to extend C-based PSIA to N and other organic elements are emerging. Two related efforts are warranted, (a) development of rapid, convenient, and sensitive methods for high-precision PSIA, a necessary precursor to (b) a concerted investigation into the relationship of metabolic state to intramolecular isotope ratio. Inherent in this latter goal is the need to identify long-lived molecules in long-lived cells that retain a record of early isotopic conditions, as has been shown for post-mortem human neuronal DNA. Using known metabolic precursor-product relationships between intramolecular positions, future studies of physiological isotope fractionation should reveal the relationship of diet and environment to observed isotope ratio. This science of isotope physiology, or simply isotopics, should add an important tool for elucidation of early factors that effect later health, probably the most difficult class of biomedical issues.