Ans. is 'b' i.e. it converts hemoglobin to methemoglobin Glutathione prevents oxidation of hemoglobin to methemoglobin.The heme group of hemoglobin contains iron in the ferrous state. Hemoglobin can accept and transport oxygen only when the iron atom is in its ferrous form. When hemoglobin becomes oxidized, it is converted to the ferric state (Fe3+) or methemoglobin. Methemoglobin is unable to transfer oxygen. Glutathione prevents this oxidation.GlutathioneGlutathione is a tripeptide of glutamic acid, cysteine, and glycine. The molecule has a sulfhydryl (-SH) or thiol group on the cysteine, which accounts for its strong electron-donating character.It exists in two forms: reduced glutathione or GSH. In the reduced state, the thiol group of cysteine is able to donate a reducing equivalent (H++ e ) to other unstable molecules, such as reactive oxygen species. In donating an electron, glutathione itself becomes reactive, but readily reacts with another reactive glutathione to form glutathione disulfide (GSSG) or oxidized glutathione. GSH can be regenerated from GSSG by the enzyme glutathione reductase.While all cells in the human body are capable of synthesizing glutathione, liver glutathione synthesis has been shown to be essential. The liver is the largest GSH reservoir.Because of its reducing property, reduced glutathione has potent antioxidant action.Functions:GSH is an extremely important cell protectant. It directly reduces reactive hydroxyl free radicals, other oxygen- centered free radicals, and radical centers on DNA and other biomoleculesGSH is the essential cofactor for many enzymes which require thiol-reducing equivalents, and helps keep redox- sensitive active sites on enzymes in the necessary reduced state. GSH is used as a cofactor bymultiple peroxidase enzymes, to detoxify peroxides generated from oxygen radical attack on biological molecules;transhydrogenases, to reduce oxidized centers on DNA, proteins, and other biomolecules; andglutathione S-transferases (GST) to conjugate GSH with endogenous substances (e.g., estrogens) and to exogenous electrophiles (e.g., arene oxides, unsaturated carbonyls, organic halides), and diverse xenobiotics.GSH is a primary protectant of skin, lens, cornea, and retina against radiation damage, and the biochemical foundation of P450 detoxication in the liver, kidneys, lungs, intestinal epithelia, and other organs.GSH acts as a carrier in transport of certain amino acids across membranes in the kidney.Glutathione (GSH) participates in leukotriene synthesis