Protometabolic Reduction of NAD⁺ with α-Keto Acids

Understanding the chemical origins of life has traditionally focused on synthesizing biologically relevant molecules from prebiotic conditions. However, the mechanisms by which energy from foodstuff breakdown could be captured and used for protocell persistence remain less explored. Prior research has shown that certain organic molecules could serve as precursors in protometabolic systems. Yet, no prior work had resolved how energy from catabolism might have been coupled to anabolic processes in early life forms. This gap motivated investigations into how redox reactions might have functioned without enzymes. The RNA world hypothesis suggests RNA molecules could have played catalytic roles. However, the specific reactivity of RNA-derived cofactors like NAD+ in protometabolic contexts had not been tested. This uncertainty drove the need to examine small organic molecules identified as potential protometabolic constituents. The study aimed to determine if such molecules could interact with NAD+ in ways that suggest prebiotic energy capture. This uncertainty required a new experimental approach to explore nonenzymatic redox chemistry.

The study aimed to investigate how energy from catabolic reactions could be captured prebiotically using RNA-derived molecules. Specifically, the researchers sought to determine if NAD+ could be reduced nonenzymatically by protometabolic precursors. The motivation was to explore whether such reactions could form the basis of a prebiotic electron transport chain. The focus was on α-keto acids like pyruvate and oxaloacetate, which are plausible prebiotic molecules. The researchers wanted to test if these acids could reduce NAD+ during oxidative decarboxylation. This approach was chosen to model how energy might have been captured in early protocells. The study aimed to assess whether RNA world components could support energy transduction. This question had not been directly addressed in prior research.

The researchers used NAD+ and α-keto acids in nonenzymatic redox reactions. They tested pyruvate and oxaloacetate as potential reductants. The experiments involved oxidative decarboxylation under prebiotically plausible conditions. FAD was included as a redox mediator in some trials. A terminal electron acceptor was used to simulate a prebiotic electron transport chain. The team monitored the consumption of α-keto acids and the reduction of NAD+. They assessed the reactivity of RNA-derived cofactors in protometabolic contexts. The setup allowed for the evaluation of energy capture mechanisms without enzymes.

NAD+ was reduced nonenzymatically by α-keto acids during oxidative decarboxylation. Pyruvate and oxaloacetate both served as effective reductants in the reactions. The presence of FAD and a terminal electron acceptor enabled a plausible electron transport chain. The observed reactivity suggests a prebiotic energy transduction mechanism. The reduction of NAD+ was rapid and consistent across multiple trials. The electron transport chain initiated by NAD+ and α-keto acids was stable under prebiotic conditions. The results indicate that RNA-derived molecules could support energy capture. These findings suggest that protometabolic systems could function without enzymes.

The findings suggest that RNA-derived molecules like NAD+ could have supported prebiotic energy transduction. The observed reactivity of NAD+ with α-keto acids indicates a plausible protometabolic pathway. The presence of FAD and a terminal electron acceptor supports a prebiotic electron transport chain. The study shows that energy from catabolism could have been captured without enzymes. The results align with the RNA world hypothesis by showing RNA-derived molecules could function in energy transduction. The observed chemistry suggests a mechanism for coupling catabolism to anabolism. These findings do not propose a complete protometabolic system but demonstrate a key reaction. The study does not claim that this pathway was the only prebiotic mechanism but shows it is plausible.