no PLANT RESPIRATION 



had been drawn up by Bach, Engler and their collaborators for 

 the processes of slow oxidation in vitro. From the preceding 

 exposition it is evident that, according to the theory of Bach- 

 Engler, the atmospheric oxygen is bound only by means of 

 autoxidators {i.e. substances which transform the saturated 

 oxygen molecule 0^0 into unsaturated — O — O — ),' and of 

 course by the formation of peroxide-like moloxides. In living 

 plant cells there have been found peroxide-like substances^ 

 which were termed oxygenases by Chodat and Bach. Whether 

 the question here is one of organic peroxides or simply hydrogen 

 peroxide does not appear to be of particular importance, since 

 the most essential oxidations in the plant cell only come to 

 pass after secondary activation of oxygenases. Substances 

 which activate oxygenases Bach and Chodat call peroxidases 

 and thereby assume that peroxidase is to be included in the 



' Bach, A. und Chodat. loc. cit.; also Kastle and Loewenhardt. Amer. Jour, of Chem. 

 26: 539. 1901; Engler und Wohler. Z. f. anorg. Chem. 29: i. 1902. [For a complete 

 account of oxidases as understood in 1909 see Kastle, J. H. The Oxidases and other Oxygen- 

 catalysts Concerned in Biological Oxidations. U. 8. Treas. Dept. Hygienic Lab. Bull. 59. 

 which also contains a valuable bibliography of 467 entries.] 



" The best-known substance of this t3^e, found in both plant and animal 

 cells, was discovered by Hopkins (Biochem. Jour. 15 : 286-305. 1921) and called 

 glutathione. Its composition is so well-known as to have been proven by 

 synthesis (Stewart and Tunnicliffe. Biochem. Jour. 19:207. 1925). It 

 represents the union of a-amino glutaric acid and a-amino, /3-thiopropionic acid 

 (hence gluta-thione) with the elimination of a molecule of water. Possibly by 

 the aid of the catalytic action of traces of iron, it is found to act as a carrier of 

 o.xygen to the o.xidisable constituents of cells, and even to fats and proteins 

 (Hopkins, F. G. Biochem. Jour. 19: 787-819. 1925). 



If GSH be taken as the symbol for the reduced form and G2S2 for the o.xidised 

 form, the action may be represented by the equation 



4GSH -t- O2 <=^ 2G2S2 + 2H2O. 



The energy of the oxidised form is available for oxidation and that of the reduced 

 form for reduction. The recent work of Kendall and Nord (J. Biol. Chem. 

 69: 295-337. 1926) has added to our knowledge of the conditions which govern 

 the equihbrium between the oxidised and reduced forms, and of the intermediate 

 "oxygen addition product" which Kendall and Nord believe to be the active 

 component of the system. The oxygen in this compound is thought to be in the 

 unsaturated form, — O — O — . 



These workers deny the catalytic role of iron in relation to glutathione but the 

 existence of such a relationship would qualify the older view of autoxidation. 

 The demonstration of glutathione and the production of evidence in favor of its 

 dependence on iron have done much to call into question the enzymatic nature 

 of the "o.xidases" as a whole. — Ed. 



