A Magnesium Binding Site And The Anomeric Effect Regulate The Abiotic Redox Chemistry Of Nicotinamide Nucleotides

Nicotinamide adenine dinucleotide (NAD⁺) is a redox active molecule that is universally found in biology. Despite the importance and simplicity of this molecule, few reports exist that investigate which molecular features are important for the activity of this ribodinucleotide. By exploiting the nonenzymatic reduction and oxidation of NAD⁺ by pyruvate and methylene blue, respectively, we were able to identify key molecular features necessary for the intrinsic activity of NAD⁺ through kinetic analysis. Such features may explain how NAD⁺ could have been selected early during the emergence of life. Simpler molecules, such as nicotinamide, that lack an anomeric carbon are incapable of accepting electrons from pyruvate. The phosphate moiety inhibits activity in the absence of metal ions but facilitates activity at physiological pH and model prebiotic conditions by recruiting catalytic Mg²⁺. Reduction proceeds through consecutive single electron transfer events. Of the derivatives tested, including nicotinamide mononucleotide, nicotinamide riboside, 3-(aminocarbonyl)-1-(2,3-dihydroxypropyl)pyridinium, 1-methylnicotinamide, and nicotinamide, only NAD⁺ and nicotinamide mononucleotide would be capable of efficiently accepting and donating electrons within a nonenzymatic electron transport chain. The data are consistent with early metabolic chemistry exploiting NAD⁺ or nicotinamide mononucleotide and not simpler molecules.