Stable nitrogen (¹⁵N/¹⁴N) and carbon (¹³C/¹²C) isotopic compositions of amino acids in organisms have widely been employed as a powerful tool to evaluate resource utilization and trophic connection among organisms in diverse ecosystems. However, little is known about the physiological factors or mechanisms responsible for determining the isotopic discrimination (particularly for carbon) within amino acids of organisms. In the present study, we investigated the inter-trophic discrimination of nitrogen and carbon isotopes within amino acids (Δδ¹⁵N_AA and Δδ¹³C_AA, respectively) using four consumer–diet pairs. Each pairing illustrates a metabolic perspective of isotopic fractionation of amino acids. The Δδ¹⁵N_AA values in these combinations reveal a trend consistent with those observed in many other combinations in previous studies. This further validates a standard scenario: the deamination preferentially removes ¹⁴N amino group from diet-derived amino acids, leaving behind the ¹⁵N-enriched amino acids in consumer biomass. The Δδ¹⁵N_AA values thus mirror the activity of amino acid deamination in consumers. In contrast, the trends in the Δδ¹³C_AA value suggest a different metabolic fate for the amino acid carbon isotope. Based on our results, we predict the following scenario: decarboxylation preferentially removes ¹²C α-carbon (i.e., carbonyl-carbon) from pyruvic acid in glycolysis, and from α-ketoglutaric acid in the tricarboxylic acid cycle, leaving behind the ¹³C-enriched both pyruvic and α-ketoglutaric acids. The ¹³C is then transferred to amino acids that are synthesized from the ¹³C-enriched precursor molecules within consumers. The Δδ¹³C_AA values therefore mirror the pathways of de novo amino acid synthesis in consumers. The proposed link between nitrogen and carbon isotopes can refine our knowledge of the potential processes affecting the isotopic fractionation within diet and consumer compartments, as well as environmental samples.

Graphical abstract

中文翻译：

---

与生物脱羧相关的同位素分馏的新见解：对生物地球科学中氨基酸同​​位素方法的启示

生物中氨基酸的稳定氮（¹⁵ N / ¹⁴ N）和碳（¹³ C / ¹² C）同位素组成已被广泛用作评估各种生态系统中生物之间资源利用和营养联系的有力工具。但是，对于决定生物体氨基酸内的同位素区分（尤其是碳）的生理因素或机制知之甚少。在本研究中，我们调查氮和碳同位素的-营养间歧视氨基酸内（Δ δ ¹⁵ Ñ _AA和Δ δ ¹³ C ^ _AA）分别使用四个消费者饮食对。每个配对都说明了氨基酸同位素分级的代谢观点。该Δ δ ^15个ñ _AA在这些组合中值显示与那些在以往的研究中许多其他的组合观察相一致的趋势。这进一步验证了一个标准方案：脱氨作用优先从饮食中的氨基酸中除去¹⁴ N氨基酸，在消费生物质中留下¹⁵ N富集的氨基酸。该Δ δ ^15个Ñ _AA值从而反映在消费者氨基酸脱氨的活性。与此相反，在Δ趋势δ ¹³ C ^ _AA值表明氨基酸碳同位素的代谢命运不同。根据我们的结果，我们预测以下情形：脱羧优先去除¹² Ç α碳上（即，羰基碳）从糖酵解丙酮酸，和从α在三羧酸循环酮戊二酸，留下后面¹³ C-富含丙酮酸和α-酮戊二酸。的¹³ C被再转移到被从合成的氨基酸¹³ C-富集的前体分子内的消费者。该Δ δ ¹³ C ^ _AA因此，数值反映了消费者中从头合成氨基酸的途径。氮和碳同位素之间的拟议联系可以完善我们对影响饮食和消费者区隔以及环境样品中同位素分级的潜在过程的了解。

图形概要