Fluoroacetate blocks the Krebs cycle by inhibiting the following enzyme

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