This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of Purines and Pyrimidines, Subject name: Biochemistry
[{'content': 'Rate limiting step in porphyrine synthesis - \nSelect and explain. \nA. ALA dehydratase, B. ALA synthase, C. UPG decarboxylase, D. Ferrochelatase', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e., ALA synthase o See above explanation. Heme is the most important porphyrin (porphyrin III) in the body.", 'role': 'assistant'}]