Phosphoglucoisomerase interconverts glucose 6 phosphate to, and from, glucose 1 phosphate.

Question

After mixing equal amounts of the two molecules, the solution achieved equilibrium at 25 ∘C. The concentration at equilibrium of glucose 1‑phosphate is 0.01 M, and the concentration at equilibrium of glucose 6‑phosphate is 0.19M.

1. Calculate the equilibrium constant, Keq
2. Calculate the standard free energy change ΔG∘, of the reaction mixture. (R = 8.314 J/Kmol)

Answer 1

Glu-6-P <==> Glu-1-P

Since equal amounts of each were present to start, and at equilibrium the [Glu-6-P] is found to be greater than that of [Glu-1-P], we can conclude the equilibrium favors Glu-6-P and can write the reaction as

Glu-1-P <==> Glu-6-P

Keq = [Glu-6-P] / [Glu-1-P] = 0.19 / 0.01

Keq = 19

∆Gº = -RT ln K

∆Gº = -(8.314 J/Kmol)(298K) ln 19

∆Gº = -2478 J/mol x 2.94

∆Gº = 7296 J/mol = 7.3 kJ/mol