The Krebs cycle involves the aerobic breakdown of glucose for energy. In the first reaction of the Krebs Cycle, the enzyme Aconitase converts Citric acid to its isomer, the molecule isocitrate. The Keq’ for this reaction is approximately 0.1. ∆G°' for this reaction is therefore and the reaction is .

The reaction is at equilibrium

Explanation:

The Krebs cycle is an aerobic pathway because the final electron acceptor required is oxygen.

The most common situation leading to a disruption in the function of Krebs cycle is the lack of oxygen to accept electrons in the electron transport chain.  

The conversion of citrate to isocitrate (isomerization), is catalyzed by the enzyme, aconitase (also known as aconitate hydratase). The hydroxyl (alcohol) group of citrate is moved to an adjacent carbon so that it can be oxidized to form a keto group.

This reaction involves generation of an enzyme-­bound intermediate, cis­aconitate. At equilibrium, there exists 90% citrate, 3% cis­aconitate, and 7% isocitrate; hence the equilibrium of aconitase lies toward citrate formation.

Although the aconitase reaction does not require cofactors, it requires ferrous (Fe2+) iron in its catalytic mechanism. This Fe2+ is involved in an iron–sulfur center, which is an essential component in the hydratase activity of aconitase.    

According to Gibb's free energy:

ΔG = 0 - Reaction at equilibrium.

ΔG > 0 - non-spontaneous reaction.

ΔG < 0 - spontaneous reaction.

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