# Does the energy from ATP hydrolysis vary among different cells?

I know that when ATP is hydrolyzed into ADP it gives 7.3 kcal/mol. The question is, does this value vary among different types of cells?

• NADH and FADH are not hydrolyzed, but they can be oxidized, and the resulting energy used to drive ATP synthesis in mitochondria. Can you give a source for your numbers? 3.7 calories (kcal / mol) for ATP hydrolysis sounds way too low. – Roland Oct 26 '17 at 17:23
• thanks for your comment. yes, you are right it oxidized and it gives 7.3, I wrote it by mistake. I will edit the question. thanks again. – Reem M.Al Haj Oct 27 '17 at 5:49
• I see, you are simply asking about the energy of ATP hydrolysis. The way you question was worded, it sounds like you were asking about the total energy from NADH and FADH2 oxidation. And you got an answer on that. I will edit to clarify. – Roland Oct 27 '17 at 5:59

First, like any chemical reaction, the free energy $\Delta G$ of ATP hydrolysis depends on the concentrations of the reactants. You can explore different values of $\Delta G$ with this calculation tool. Typical values are [ATP] = 10 mM, [ADP] = 1 mM and [P$_i$] = 20 mM, which gives $\Delta G$ = 42 kJ/mol (10 kcal/mol). But all these concentrations can vary between cells, and there is not much data available on intracellular concentrations in specific cell types. Many textbooks give free energy values denoted $\Delta G^{\circ}{'}$ which are calculated at concentrations of 1M, which is of course completely unphysiological.
In addition, the $\Delta G$ is strongly affected by the concentration of Mg$^{2+}$, because this ion associates with phosphate groups and alters their free energy. It also depends on pH, since the phosphate groups can take up/release protons. If you are interested, an in depth analysis is found here.