GLUTATHIONE 147 



is that of a dipeptide of cystein and glutamic acid and is 

 represented by the formula 



CH 2 - SH 



I 



CH . NH . CO . CH, . CH, . CHNH, . COOH 



I 

 COOH 



This substance, when oxidized by the removal of the 

 hydrogen between two molecules, yields the compound 



CHj - s s - CH. 



I I 



CH . NH . CO . CH 2 . CH a . CHNH 2 . COOH CH . NH . CO . CH 2 . CH. . CHNH. . COOH 

 COOH COOH 



For simplicity of expression these changes may be repre- 

 sented as follows : — ■ 



-2H 



2GSH ^ GS . SG 

 + 2H 



In its oxidized form, GS . SG, it serves as an acceptor 

 of the hydrogen set free from, say, succinic acid by the de- 

 hydrase which occurs in minced muscle, giving rise to the 

 reduced form, GSH, but it is not by itself able to remove this 

 hydrogen in the absence of the enzyme succinic acid dehy- 

 drase. The reduced form is then ready to give up its hydrogen 

 to oxygen activated by iron with the formation of GS . SG 

 and water. The optimum pH for the reaction involving the 

 removal of hydrogen 



2GSH -> GS . SG + 2H 



is 7-4, and at pH 6 it is much retarded, and below this the 

 reduced form GSH is stable ; on the other hand, the accept- 

 ance of hydrogen by the oxidized form 



GS. SG + 2H^ 2GSH 



is much the same at pH 6 and pH 7-4. 



The question whether glutathione is able to act in the 

 absence of metals has been much discussed, and it would ap- 

 pear that the balance of evidence is in favour of an essential part 

 being played by iron ; this could be explained by assuming 

 that its function is to activate the oxygen, as postulated by 

 Warburg, previous to its oxidising the hydrogen 



2GSH + O = GS . SG + H 2 0. 



IO* 



