This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
[{'content': 'The cyclic AMP is inactivated by the action of which specific enzyme? \nSelect and explain. \nA. Phosphodiesterase, B. Phosphate, C. Protein kinase, D. Adenyl cyclase', 'role': 'user'}, {'content': "Answer: A \nExplanation: cAMP undergoes rapid hydrolysis catalysed by the enzyme phosphodiesterase, to 5'AMP which is inactive. Caffeine and theophylline can inhibit phosphodiesterase and increase the intracellular levels of cAMP.", 'role': 'assistant'}]