Question

Which of the following is correct sequence in Krebs cycle?

• A. Isocitric acid$\to$Oxalosuccinic acid$\to$ $\alpha$-ketoglutaric acid
• B. Oxalosuccinic acid $\to$Isocitric acid$\to$ $\alpha$-ketoglutaric acid
• C. $\alpha$ -ketoglutaric acid $\to$Isocitric acid$\to$Oxalosuccinic acid
• D. Isocitric acid$\to$ $\alpha$ -ketoglutatric acid $\to$ Oxalosuccinic acid

Answer 1

The correct option is A Isocitric acid$\to$Oxalosuccinic acid$\to$ $\alpha$-ketoglutaric acid

Citric acid undergoes dehydration to form cis-aconitase which then undergoes hydration reaction to form isocitrate. Oxidative decarboxylation of citric acid into alpha-ketoglutarate catalyzed by Isocitrate dehydrogenase enzyme forms an unstable intermediate oxalosuccinic acid (6C) which immediately undergoes decarboxylation and forms alpha-ketoglutarate. Thus, the correct answer is option A.