Question

Arginine kinase catalyzes the following reversible reaction:

phosphoarginine + ADP <======> arginine + ATP

a. What is the K_eqfor the reaction at 25^oC when the equilibrium concentrations are as follows?

phophoarginine: 0.737 mM

ADP: 0.750 mM

arginine: 4.78 mM

ATP: 3.87 mM

b.         What is the value of ΔG^o’for the reaction? In which direction does it occur spontaneously?

Answer 1

consider the given reaction

phosphoarginine + ADP --> Arginine + ATP

the equilibrium constant is given by

Keq = [Arginine] [ATP] / [ADP] [phosphoarginine]

using the given concentrations

Keq = [4.78 x 10-3 ] [3.87 x 10-3] / [0.75 x 10-3] [0.737 x 10-3]

Keq = 33.4665

so

the value of Keq is 33.4665

b)

now

we know that

dGo = -RT lnKeq

dGo = -8.314 x 298 x ln 33.4665

dGo = -8697.6 J

dGo = -8.6976 kJ

we know that

for a reaction to be spontaneous in the forward direction , dGo < 0

in this case dGo < 0

so

the reaction is spontaneous in the forward direction