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Biogeosciences
202408202408
Regulation of nitrogen isotopic ratios of cellular components
Naohiko Ohkouchi, Yuta Isaji, Nanako O. OgawaNaohiko Ohkouchi, Yuta Isaji, Nanako O. Ogawa
Cell, Nitrogen isotopic ratio, Amino acids, Chlorophylls
A simplified, autonomously regulated cellular model for understanding the discrimination of nitrogen isotopes in organisms. ‘AA’ denotes amino acid pool in vivo. Nitrogen isotopic ratios of diet (d), temporal pool of amino acids (AA), protein reservoir (p), and excrement (ex) are denoted by δd, δAA, δp, and δex, respectively. Flows of nitrogen denoted by f and isotope effects by ε. The isotopic ratios of nitrogen transferred the indicated pathways are given in the form δ – ε.
This paper is an attempt to generalize the nitrogen isotope information of the molecules that make up the cell from our point of view. Nitrogen in the cell exists as 20 proteinaceous amino acids, nucleobases, hemes, chlorophylls, and others, and their composition is similar among organisms. Based on a physiologically simple autonomous system that maintains a balance between inputs and outputs, it is theoretically predicted that 15N is distributed to each cellular compound with a certain regularity, and thus a specific relationship in nitrogen isotopic ratios among compounds. Previous studies essentially confirm this. The nitrogen isotopic ratio of compound i constituting the cell can be generalized as
δ15Ni = δ15Nplant + Δi (TP − 1) + γi
where TP represents the trophic position, and Δi and γi are the trophic discrimination factor and the intracellular 15N distribution of compound i, respectively. Knowing reliable values of Δi and γi will help us to better understand nitrogen dynamics in the biosphere and advance our understanding of the picture of the Earth’s environment through biogeochemistry.
