代谢货币耦合中的热力学成本可控性权衡
Thermodynamic cost-controllability tradeoff in metabolic currency coupling
AI总结：
本文研究了代谢货币物质在不同能量状态间的耦合对代谢调控效率和生物进化的影响，提出了一种理论模型揭示了代谢可控性与热力学成本之间的根本权衡关系。
摘要：
细胞代谢由多种货币代谢物如ATP、GTP和NAD(P)H全局调控。这些代谢物在带电（高能）和不带电（低能）状态间循环以介导能量转移。尽管不同的货币代谢物与不同的代谢功能相关，但它们的带电和不带电形式通常通过生化反应如ATP+GDP⇌ADP+GTP和NADP++NADH⇌NADPH+NAD+相互转换。因此，它们的能量状态通常耦合并相互影响，这会阻碍不同货币代谢物的独立调控。尽管对个体货币代谢物的分子生物学知识已经很丰富，但如何协调各种耦合的货币代谢物以塑造代谢调控、效率以及最终生物体的进化仍知之甚少。本文提出了一种代谢货币耦合的最小理论模型，并揭示了代谢可控性与热力学成本之间的根本权衡关系：增加对多种货币代谢物独立调控的能力通常需要这些代谢物具有相当的丰度，这反过来又会导致更高的熵生产率。这种权衡表明，在复杂环境中，生物体进化上倾向于使货币代谢物具有相等的丰度以提高代谢可控性，但以更高的热力学成本为代价；相反，在简单环境中，生物体会进化出不平衡的丰度以减少热量散失。这些考虑还提出了关于核苷酸池平衡和基因组GC含量进化趋势的假说。
英文摘要：
Cellular metabolism is globally regulated by various currency metabolites such as ATP, GTP, and NAD(P)H. These metabolites cycle between charged (high-energy) and uncharged (low-energy) states to mediate energy transfer. While distinct currency metabolites are associated with different metabolic functions, their charged and uncharged forms are generally interchangeable via biochemical reactions such as ${\rm ATP{\,+\,}GDP{\,\rightleftharpoons\,}ADP{\,+\,}GTP}$ and $\rm NADP^+{\,+\,}NADH{\,\rightleftharpoons\,}NADPH{\,+\,}NAD^+ $. Thus, their energetic states are generally coupled and influence each other, which would hinder the independent regulation of different currency metabolites. Despite the extensive knowledge of the molecular biology of individual currency metabolites, it remains poorly understood how the coordination of various coupled currency metabolites shapes metabolic regulation, efficiency, and ultimately the evolution of organisms. Here, we present a minimal theoretical model of metabolic currency coupling and reveal a fundamental tradeoff relationship between metabolic controllability and thermodynamic cost: increasing the capacity to independently regulate multiple currency metabolites generally requires comparable abundances of those metabolites, which in turn incurs a higher entropy production rate. The tradeoff suggests that in complex environments, organisms evolutionarily favor an equal abundance of currency metabolites to enhance metabolic controllability at the expense of a higher thermodynamic cost; conversely, in simple environments, organisms evolve to have imbalanced amounts of them to reduce heat dissipation. These considerations also offer a hypothesis regarding evolutionary trends in nucleotide-pool balance and genomic GC content.
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