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
In the Krebs cycle, Malonate competitively inhibits 
Select and explain. 
A. Isocitrate dehydrogenase, B. Succinate thiokinase, C. Succinate dehydrogenase, D. a-Ketoglutarate dehydrogenase
C: Succinate dehydrogenase
Answer: C: Succinate dehydrogenase 
Explanation: The first dehydrogenation reaction, forming fumarate, is catalyzed by succinate dehydrogenase, which is bound to the inner surface of the inner mitochondrial membrane. The enzyme contains FAD and iron-sulfur (Fe-S) protein, and directly reduces ubiquinone in the electron transpo chain. This is inhibited by Malonate Reference: Harper; 30th edition; Page no: 163