Question 21.4: The hydrolysis of succinyl-SCoA is coupled with the producti...
The hydrolysis of succinyl-SCoA is coupled with the production of GTP. The equations for the reactions are given below. Combine the equations appropriately and determine if the coupled reaction is favorable.
Succinyl-SCoA → Succinate + SCoA ΔG = -9.4 kcal/mol
GDP + HOPO_3 ^{2-} + H^+ \longrightarrow GTP + H_2O ΔG = +7.3 kcal/mol
ANALYSIS Add the two equations together to produce the equation for the coupled reaction. Also add the ΔG values together, paying close attention to the signs. If the ΔG is positive, the reaction is not favorable and will not occur; if the ΔG is negative, the reaction is favorable and will occur.
Succinyl-SCoA + GDP + HOPO_3 ^{2-} + H^+ \longrightarrow Succinate + GTP + H_2 ΔG = -2.1 kcal/mol
Since ΔG is negative, the coupled reaction will occur as written.