0x668143c4…385fsent to0xf55a45a8…9aae·#13,051,568·0x42b76ece…7ca98d
The triphosphate tail of ATP binds into the "p-loop motif" at the ATP protein binding site on protein. The bonds here are hydrogen bonds, assumed to use the (deprotonated) hydroxyl group on ATP as the bond acceptor.
I think it is actually the bond donator. But this requires that it is fully protonated.
The hydrogen donor in a hydrogen bond is electron withdrawing , whereas the acceptor is "electron donating".
The following model resolves why a negatively charged molecule like ATP could be "electron withdrawing", like Gilbert Ling said.
I want ATP to be fully protonated so that it can store the cathode for the electrical circuits of the cell, H+, after it is displaced from the surface phase (H3O2-)n by K+, because K+ is able to bind more strongly. This increases the distance from the anode to the cathode reaction, it places a "wire" between them. It extends the electrical circuit.
Compared to a protonated group, deprotonated groups are clearly less negatively charged. Because they can't hold onto a proton, while the protonated can. The acceptor in a hydrogen bond, should favourably be the atom with the most negative charge. This is a good start. But, the unprotonated lacks a proton, so it is "relatively" more charged. But what if that proton was re-introduced again?
While the negative charge of the deprotonated hydroxyl groups in ATP might not be enough to hold onto a proton, the added charge of the hydrogen bond acceptors in the protein binding site & both acting on the proton together, might.
Like, a "lock in key" fit for.... a proton. With it, ATP outside protein binding site is _not_ protonated. It only stores protons when it is bound, ensuring their release when it is hydrolysed. And because it stores protons, it also becomes "electron withdrawing", via the hydrogen bonds, of which there are many.
So, the p-loop/ATP complex is acting like a base, using a lock-in-key fit for... protons. And it is why ATP is electron withdrawing.