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': 'In cytochrome P450, P stands for: \nSelect and explain. \nA. Pigment, B. Polymer, C. Structural proteins, D. Substrate protein', 'role': 'user'}, {'content': "Answer: A \nExplanation: Cytochrome P450:\nThe main reaction involved in phase 1 metabolism is hydroxylation, catalyzed by a family of enzymes known as monooxygenases or 'mixed-function oxidases.'\xa0\n\nThere are at least 57 cytochrome P450 genes in the human genome.\xa0\nCytochrome P450 is a heme enzyme.\xa0\nThey exhibit an absorption peak at 450 nm.\xa0\nApproximately 50% of the common drugs that humans ingest are metabolized by isoforms of cytochrome P450.\xa0\nThey also act on steroid hormones, carcinogens and pollutants.\xa0\nIn addition to their role in metabolism of xenobiotics, cytochrome\xa0P450 are important in the metabolism of a number of physiological compounds — for example, the synthesis of steroid hormones and the conversion of vitamin D to its active metabolite, calcitriol.\xa0\nNADPH is required to reduce cytochrome P450.\xa0\nLipids which are components of cytochrome P450 is phosphatidyl choline.", 'role': 'assistant'}]