Enthalpy of Hydrolysis of the 3′ Bond of Adenosine 3′, 5′-Monophosphate and Guanosine 3′, 5′-Monophosphate

The enthalpy of hydrolysis of the 3' bond of adenosine 3',5'-monophosphate has been measured calorimetrically and found to be -14,100 cal per mole.This value is close to that which has been reported for the free energy of hydrolysis of the same bond.The enthalpy of hydrolysis of the 3' bond of guanosine 3',5'-monophosphate is substantially lower, but still indicative of a high energy bond, being -10,500 cal per mole.Although cyclic adenosine 3', 5'monophosphate is very widely distributed in nature and mediates the actions of a substantial number of hormones, little is known about its thermodynamic properties or mechanism of action.Recently, however, the free energy of hydrolysis of the 3' bond of cyclic AMP' was determined and found to be extremely high, namely in the range of -11,000 to -12,000 cal per mole (1).In view of this high value (about 3,000 cal greater than that of the free energy of hydrolysis of the terminal phosphate group of ATP determined under similar conditions (2)), it seemed of considerable interest to determine the relative contribution of the enthalpy and the entropy changes to the free energy of hydrolysis of cyclic AMP.For purposes of comparison, the enthalpy of hydrolysis of the 3' bond of cyclic GMP has also been determined.Methods