Regulation of nitrogen isotopic ratios of cellular components

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 δ¹⁵N_i = δ¹⁵N_plant + Δ_i (TP − 1) + γ_i, where TP represents the trophic position, and Δ_i and γ_i are the trophic discrimination factor and the intracellular ¹⁵N distribution of compound i, respectively. Knowing reliable values of Δ_i and γ_i 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.