The image designed by Sphere Studio is selected as the Cover of Nature Catalysis in March.
Formate dehydrogenase is immobilized on a scanning tunnelling microscope tip to measure the kinetic turnover of its enzymatic reaction showing that the bound NADH directly converts to NAD+ via in situ hydride exchange.
Understanding the mechanisms and kinetics of enzymatic reactions is essential for studies of life science and for bioengineering. Here the different reaction states in the catalytic cycle of formate dehydrogenase have been distinguished by their characteristic conductances, using the scanning tunnelling microscope break-junction technique, and these conductances have been further exploited as markers to monitor the catalytic mechanism of formate dehydrogenase from Candida boidinii. Combined with multiscale simulations, we demonstrate that the bound reduced form of nicotinamide adenine dinucleotide (NADH) converts to nicotinamide adenine dinucleotide (NAD+) directly via a hydride-transfer reaction in situ during the catalytic cycle of formate dehydrogenase. This conversion does not proceed via the apoenzyme state invoked in the conventional, generally accepted Theorell–Chance mechanism. This work provides intriguing insight into the mechanism of formate dehydrogenase and highlights the potential of the single-molecule technique in revealing the catalytic mechanism of NADH/NAD+-dependent oxidoreductases.
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