Identifying apparent local stable isotope equilibrium in a complex non-equilibrium system

Journal Article · 30 January 2018 · Rapid Communications in Mass Spectrometry

DOI: https://doi.org/10.1002/rcm.8040 · OSTI ID:1543484

He, Yuyang  ^[1]; Cao, Xiaobin ^[1]; Wang, Jianwei ^[1]; Bao, Huiming ^[1]

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1. Louisiana State Univ., Baton Rouge, LA (United States). Dept. of Geology and Geophysics

Although being out of equilibrium, biomolecules in organisms have the potential to approach isotope equilibrium locally because enzymatic reactions are intrinsically reversible. A rigorous approach that can describe isotope distribution among biomolecules and their apparent deviation from equilibrium state is lacking, however. Applying the concept of distance matrix in graph theory, we propose that apparent local isotope equilibrium among a subset of biomolecules can be assessed using an apparent fractionation difference (|Δα|) matrix, in which the differences between the observed isotope composition (δ') and the calculated equilibrium fractionation factor (1000lnβ) can be more rigorously evaluated than by using a previous approach for multiple biomolecules. We tested our |Δα| matrix approach by re-analyzing published data of different amino acids (AAs) in potato and in green alga. Our re-analysis shows that biosynthesis pathways could be the reason for an apparently close-to-equilibrium relationship inside AA families in potato leaves. Different biosynthesis/degradation pathways in tubers may have led to the observed isotope distribution difference between potato leaves and tubers. The analysis of data from green algae does not support the conclusion that AAs are further from equilibrium in glucose-cultured green algae than in the autotrophic ones. Application of the |Δα| matrix can help us to locate potential reversible reactions or reaction networks in a complex system such as a metabolic system. The same approach can be broadly applied to all complex systems that have multiple components, e.g. geochemical or atmospheric systems of early Earth or other planets.

• Research Organization: Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States). National Energy Research Scientific Computing Center (NERSC)
• Sponsoring Organization: USDOE
• OSTI ID: 1543484
• Journal Information: Rapid Communications in Mass Spectrometry, Journal Name: Rapid Communications in Mass Spectrometry Journal Issue: 4 Vol. 32; ISSN 0951-4198
• Publisher: WileyCopyright Statement
• Country of Publication: United States
• Language: English