This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory chain, Subject name: Biochemistry
In TCA cycle, CO2 is released from 
Select and explain. 
A. Thioinase, B. Isocitrate dehydrogenase, C. Citrate dehydrogenase, D. Alpha ketoglutrate
D: Alpha ketoglutrate
Answer: D: Alpha ketoglutrate 
Explanation: During the citric acid cycle, two carbon dioxide molecules are removed in the following reactions: A. Step 3, isocitrate (oxalosuccinate) to alpha-ketoglutarate catalyzed by isocitrate dehydrogenase B. Step 4, alpha-ketoglutarate to succinyl CoA.it is from substrate co2is raised..not from enzymes. They are just catalyzing the reaction.Ref: MN Chatterjea Textbook of Medical Biochemistry, 8th Edition, Page no: 219