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
All are TRUE about glutathione, EXCEPT: 
Select and explain. 
A. It is a tripeptide, B. It conves hemoglobin to methemoglobin, C. It conjugates xenobiotics, D. It is a cofactor of various enzymes
B: It conves hemoglobin to methemoglobin
Answer: B: It conves hemoglobin to methemoglobin 
Explanation: Glutathione is a tripeptide. It is synthesized from -glutamic acid, cysteine, and glycine. Glutathione exists in the cell as oxidized (GSSG) or reduced (GSH) forms, and the ratio of GSH:GSSG is critical in maintaining a cellular environment in the reduced state. In addition to affecting xenobiotic conjugation with GSH, a severe reduction in GSH content can predispose cells to oxidative damage, a state that has been linked to a number of human health issues. Glutathione prevents oxidation of hemoglobin to methemoglobin. Ref: Gonzalez F.J., Coughtrie M., Tukey R.H. (2011). Chapter 6. Drug Metabolism. In L.L. Brunton, B.A. Chabner, B.C. Knollmann (Eds), Goodman & Gilman's The Pharmacological Basis of Therapeutics, 12e.