Question

If we ignore all the biological significans for a while, ATP hydrolysis, the reaction: ATP + H2O -> ADP + Pi is still a chemical reaction that must go through transition state to yield product. This is no doubt a nucleophillic substitution reaction that, according to all the paper I've found, occurs by SN2 mechanism. But what's totally missing is the energy of activation of the uncatalyzed reaction. There are a lot of paper on the mechanism of ATP hydrolysis in the active site of this enzyme and that motor. There are a few paper on uncatalyzed reaction and various nucleophile. A few paper does estimate the activation energy of ATP hydrolysis by various enzyme and motor proteins. But I haven't found a single paper estimating the Eact of the uncatalyzed reaction. My failure apart, what is the energy of activation of this reaciton without the aid of any enzyme or other catalyst? Did nobody make any estimation?

Answer 1

The exact activation energy for uncatalyzed ATP hydrolysis (ATP to ADP + Pi) is not commonly found in literature, as most research focuses on enzyme-catalyzed reactions. ATP hydrolysis spontaneously releases free energy, which is used in biological processes through energy coupling, to drive other reactions. Under standard conditions, the ΔG for ATP hydrolysis is approximately -7.3 kcal/mol (-30.5 kJ/mol), with a greater value within living cells.

Step-by-step explanation:

The question concerns the uncatalyzed chemical reaction where ATP hydrolysis results in ADP and inorganic phosphate (Pi), specifically the activation energy (Eact) required for this reaction without any enzyme or catalyst. Although finding the exact value in literature might be challenging due to the prevalence of studies focusing on enzyme-catalyzed reactions, what is known is that ATP is a highly unstable molecule that will spontaneously dissociate into ADP and Pi, releasing free energy. This energy is utilized in various biological processes through energy coupling, where the exergonic reaction of ATP hydrolysis drives endergonic reactions. Enzymes lower the activation energy for such reactions, making them proceed much more rapidly than they would without a catalyst. In the case of the sodium-potassium pump, for instance, the hydrolysis of ATP is directly coupled to the pumping of sodium and potassium ions across the cell membrane.

While the exact uncatalyzed activation energy for ATP hydrolysis is not explicitly mentioned in the provided information, the reaction's energetics are well-established under standard and physiological conditions. Under standard conditions, the ΔG for hydrolyzing one mole of ATP is approximately -7.3 kcal/mol (-30.5 kJ/mol), while in a living cell, it is close to -14 kcal/mol (-57 kJ/mol), indicating a considerable release of free energy upon ATP hydrolysis.