Question

Predict whether creatine kinase will operate in the direction of ATP synthesis or phosphocreatine synthesis at 25°C when [ATP] = 4 mM, [ADP] = 0.15 mM, [phosphocreatine] = 2.5 mM and [creatine] = 1 mM. Show your work.

Answer 1

We consider the reaction,

ATP + creatine <-----> phosphocreatine + ADP

We know that delta G⁰ for this reaction is 12.6 kJ / mol

delta G for the reaction = delta G⁰ + RT ln ([phosphocreatine] [ADP] / [ATP] [creatine])

=> delta G = (12.6) + (8.314 x 298) x ln (2.5 x 0.15 / 4 x 1)) / 1000

=> delta G = 12.6 - 5.9 = 6.7 kJ / mol

delta G for the reverse reaction will be - 6.7 kJ/mol

We know that the reaction is favoured in the direction for which delta G is negative.

=> Reaction will proceed in the opposite direction, i.e in the direction of ATP synthesis