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
In glutathione which amino acid is reducing agent 
Select and explain. 
A. Glutamic acid, B. Glycine, C. Cysteine, D. Alanine
C: Cysteine
Answer: C: Cysteine 
Explanation: The sulphydryl (-SH) group of cysteine residue is the reactive portion of glutathione which can undergo oxidation and reduction.