Experimental Determination of AG" for ATP Hydrolysis A direct measurement of the standard free-energy change associated with the hydrolysis of ATP is technically demanding because the minute amount of ATP remaining at equilibrium is difficult to measure accurately. The value of AG" can be calculated indirectly, however, from the equilibrium constants of two other enzymatic reactions having less favorable equilibrium constants: Glucose 6-phosphate + HO glucose + P Keq = 270 ATP + glucoseADP + glucose 6-phosphate Keq = 890 Using this information for equilibrium constants determined at 25 C, calculate the standard free energy of hydrolysis of ATP.