The Enthalpy Change on Adenosine Triphosphate

The energetics of ATP’ hydrolysis to ADP and P have been studied previously by combining either thermal (1, 2) or free energy (3-6) data for a number of chemical reactions according to the usual procedures of chemical thermodynamics. Such calculations, however, suffer from the fact that the uncertainties in each measurement are compounded in the final result. The ATPase properties of myosin offer a more direct method for measurement of the enthalpy change on hydrolysis of ATP. In the present paper we submit measurements which, together with data on the heat of neutralization of the buffer system employed, show that the heat evolved during hydrolysis of ATP is approximately half the value 12 kilocalories per mole which has been hitherto accepted.