ATP

ATP-generating processes include glycolysis, the citric acid cycle (TCA cycle) and oxidative phosphorylation. Glycolysis breaks glucose down into pyruvate through a series of "preparatory" and "payoff" reactions, producing 2 ATP, 2 NADH and 2 pyruvate molecules from one glucose molecule. Under anaerobic conditions, such as strenuous exercise in muscle, or in cells lacking mitochondria such as red blood cells, pyruvate is reduced to lactate by lactate dehydrogenase, in order to oxidize NADH back to NAD+. This allows glycolysis to continue but yields only 2 ATP per glucose molecule (Warburg effect exploited by cancer cells). In the presence of oxygen, pyruvate can enter the mitochondria and be converted to acetyl-CoA by pyruvate dehydrogenase, yielding NADH. Acetyl-CoA feeds into the citric acid cycle where it is completely oxidized to carbon dioxide and water. Each turn of the cycle generates 3 NADH, 1 FADH₂, 1 ATP/GTP, and 2 CO₂ molecules, while several intermediates like succinate dehydrogenase and fumarate hydratase serve as tumor suppressors. Oxidative phosphorylation couples the electrons of NADH and FADH₂ to the creation of ATP through the electron transport chain (complexes I - IV), establishing a proton gradient across the inner membrane of mitochondria. ATP synthase (F₀F₁ complex) utilizes this gradient (proton motive force) to drive the synthesis of ATP from ADP. Approximately 3 ATP are synthesized per oxidized NADH and 2 ATP per oxidized FADH₂. This concept, known as chemiosmotic theory, allows for the direct production of ATP, which can then leave the mitochondria via adenine nucleotide translocase.

Fig. 1 Schematic representation of mechanisms of ATP synthesis and storage inside the cell. (Bonora M, et al. 2012)

Adenosine triphosphate (ATP) is a crucial biomolecule that provides cellular energy for various bioprocesses. Recently, ATP was identified as a hydrotrope destabilizing protein coacervates. Researchers investigated the effects of ATP and related small molecules (adenine, adenosine, adenosine monophosphate (AMP) and triphosphate (TP)) on macromolecular phase transition (poly(N-isopropylacrylamide)) to understand the molecular mechanism behind the hydrotropic action of ATP. A multi-instrumental approach based on Lower Critical Solution Temperature (LCST), Hydrogen-Nuclear Magnetic Resonance (1H NMR) and ATR Fourier-Transform InfraRed(ATR-FTIR), solvation shell spectroscopy, and all-atom molecular dynamics simulations was employed. We found that adenine and adenosine do not affect the macromolecule solubility significantly, whereas ATP, AMP, and triphosphate displayed predominant salting-out behavior, which promoted neutral macromolecule aggregation. ATR-FTIR studies support the salting-out behavior of ATP at biologically relevant (<0.1 M) concentrations. Consistently, we observed no specific binding interaction between the macromolecule and ATP in spectroscopic experiments as well as in MD simulations. At high concentrations, ATP self-aggregates into nanoclusters, which leads to destabilization of the PNIPAM chain in its collapsed state. Altogether, we show that disorder of neutral macromolecules containing valine like pendant group (isopropyl group) is not solely responsible for the hydrotropic action of ATP, and ATP rather stabilizes such macromolecules via the excluded volume effect at physiological concentrations.

Fig. 2 ATP can stabilize neutral macromolecules with an excluded volume effect at physiological concentrations. (Ayvaz C, et al. 2025)