This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of carbohydrate, Subject name: Biochemistry
Fluoroacetate blocks the Krebs cycle by inhibiting the following enzyme 
Select and explain. 
A. Citrate synthase, B. Aconitase, C. a-KG dehydrogenase, D. Succinate dehydrogenase
B: Aconitase
Answer: B: Aconitase 
Explanation: The poison fluoroacetate is found in some of the plants, and their consumption can be fatal to grazing animals. Some fluorinated compounds used as anticancer agents and industrial chemicals (including pesticides) are metabolized to fluoroacetate. It is toxic because fluoroacetyl-CoA condenses with oxaloacetate to form fluorocitrate, which inhibits aconitase, causing citrate to accumulate.Reference: Harper&;s Biochemistry; 30th edition; Chapter 16; The Citric Acid Cycle: The Central Pathway of Carbohydrate, Lipid & Amino Acid Metabolism