This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: FMGE 2019, Subject name: Biochemistry
Allopurinol inhibits which enzyme? 
Select and explain. 
A. Xanthine oxidase, B. Kinase, C. Lysyl oxidase, D. Cyclooxygenase
A: Xanthine oxidase
Answer: A: Xanthine oxidase 
Explanation: Allopurinol inhibits Xanthine oxidase Mechanism-based inhibition/Suicidal inhibitors resemble the actual substrate of the enzyme. Enzymes binds to suicidal inhibitor & catalytic process is staed. In the process of catalysis, enzyme undergoes irreversible covalent modification by the inhibitor & active enzyme can't be regenerated. (Enzyme catalyses its own destruction) Suicidal Inhibitor Enzyme Allopurinol Xanthine oxidase Aspirin Cyclooxygenase 5-FU Thymidylate synthase Penicillin Transpeptidase Difluoromethylornithine Ornithine decarboxylase