Glutathione, Structure and Biochemical Functions

Closely related to the reducing activity of the thiol group is its chemical, nucleophilic activity, which can work in the absence or the presence of enzymes (thioltransferases). Thus disulfide bonds both in homogenous (R = R ) as well as 

A key enzyme in protection against oxygen toxicity is glutathione peroxydase, a seleno-enzyme already mentioned on p. 10 which catalyzes the decomposition of hydrogen peroxide or organic hydroperoxides according to the reaction of Fig. 10. 

In order to be recycled, GSSG has to be reduced by glutathione reductase. The mechanism of the reaction has been resolved mainly by X-ray diffraction studies [15]. From the juxtaposition of the reactive moiety, it appears that the electrons from dihydroflavin adenine dinucleotide (FADH) will reduce an intramolecular disulfide bond in the enzyme forming 2 SH-groups which in turn will reduce the GSSG disulfide. 

Similarly, GSH is a cofactor in the enzymatic oxidation of the toxic formaldehyde. Here, the 5-methylol—GSH adduct is oxidized by NAD, the S-formyl intermediate hydrolyzed yielding GSH and formic acid. 

Conjugation with GSH also functions at the formation of leukotrienes, mediators of inflammatory and anaphylactic reactions. Leukotriene A, an epoxide derived from arachidonic acid, reacts with GSH to form the conjugate, leukotriene C4 (LTCJ. By the action of y-glutamyl transpeptidase, an enzyme that transfers the y-glutamyl moiety of GSH to other amino acids, leukotriene D responsible for slow anaphylaxis is formed. Further hydrolysis by dipeptidase 

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