Glutathione is a tripeptide consisting of glutamic acid, cysteine, and glycine; it is abundant in human erythrocytes as well as in many types of tissue. Reduced glutathione (GSH) acts as a reducing agent in tissues because its side-chain –SH group can be readily oxidized to form disulfide bonds. Unless glutathione is maintained substantially in its reduced form as opposed to its oxidized form in erythrocytes, they lose their ability to transport oxygen effectively. Why do you think this is so?