ADP

By Jessica L. Schommer

The ADP molecule plus inorganic phosphate are the reaction products of ATP hydrolysis, and is equally as important to the biological world as ATP. The charge density on ATP is larger than its hydrolysis product, ADP and theoretical studies show that ATP is more hydrated than ADP through the semi-empirical heat of formation calculations. ATP is used to transfer the terminal phosphate group to a substrate in a coupled ox/phos. reaction. It is important to remember that ADP is less stable in solution than ATP if an enzyme catalyst is not present to drive hydrolysis, as can also be seen from the heat of formation in solution for ADP versus ATP. ADP is necessary to form more ATP in the body, so that ox/phos. and protein synthesis can continue to occur.

Original Settings

Spin off

Space fill model

Phosphorus in Green

Carbons in Yellow

Hydrogen in Blue

Oxygen in Red

Dot Surface

A Spartan calculation showed the semi-empirical heat of formation for ADP to be -911.55 kcal/mol in a water solution.

ATP is 368.72 kcal/mol more stable in water than ADP!!

A map of the electrostatic potential helps to visualize why the ADP form is actually more unstable in a water solution.