Question

The standard free energy (AG°') of the creatine kinase reaction is –12.6 kJ.mol-1. The AG value of an in vitro creatine kinase reaction is –0.1 kJ.mol-?. At the start of the reaction, the concentration of ATP is 5 mM, the concentration of creatine is 17 mM, and the concentration of creatine phosphate is 25 mM. Using the values given, calculate the starting concentration of ADP in nanomolar. [ADP) = 18.38 [ADP] = 18.38 nM

Answer 1

Creatine kinase reaction :

Creatine + ATP $\rightleftharpoons$ Creatine-phosphate + ADP

we have $\Delta$G^o and $\Delta$G (in vitro ) , T is not given we take as = 298 K (1 mM = 10^-3 M)

we have, $\Delta$G =$\Delta$G^o+ RT ln Q

$\Delta$G =$\Delta$G^o+ RT ln ( [ADP][creat.-P] / [ATP][creat.])

-0.1 kJ/mol = -12.6 kJ/mol+ (8.315 J/mol -K)(298 K) ln ( [ADP][25*10^-3]./ [5*10^-3][17*10^-3] )

12.5 kJ/mol = (8.315 J/mol -K)(298 K) ln ( [ADP][25*10^-3]./ [5*10^-3][17*10^-3] )

ln ( [ADP][25*10^-3]./ [5*10^-3][17*10^-3] ) = 5.0453

( [ADP][25*10^-3]./ [5*10^-3][17*10^-3] ) = 155.3

so, starting, [ADP] = 0.528 M = 5.28*10⁸ nM