REDUCTASE 89 



THE REDUCING MECHANISM. 



If the formation of nitrite is the first stage in the synthesis 

 of proteins, the question arises as to the mechanism in the 

 plant which effects the reduction of nitrate to nitrite. The 

 reduction may be due to the action of an organic " reductase," 

 or it may be a photochemical reaction. If it be the latter, 

 the process must take place in the subaerial parts, essentially 

 in the leaves, and since proteins are formed in structures far 

 removed from light, it follows that the nitrite must be removed 

 to those places where the elaboration is taking place. This 

 presents certain difficulties, but is not altogether to be dis- 

 missed since nitrite has been detected in stem and roots. 

 Also nitrite has been found in the sap exuded by root pressure 

 from the cut ends of the fuchsia and the vine,* but since the 

 flow of sap is upwards, the observations have, in all probability, 

 no bearing on the immediate problem, although they indicate 

 that the reduction of nitrate to nitrite occurs in the root, where 

 it is dark, as has been found by Thomas f in Pyrus mains. 



Considering now the evidence. 



" Reductase:' — The ability of the plant to convert nitrate 

 into nitrite was first observed by Laurent, $ and later, Irving 

 and Hankinson,§ working on Elodea, came to the conclusion 

 that nitrite must be an intermediate compound in the meta- 

 bolism of nitrates. 



Kastle and Elvove || were the first to show that the ex- 

 pressed sap of potato tubers and etiolated shoots, and the 

 sap of other plants, was able to effect the change from nitrate to 

 nitrite, especially in the presence of acetaldehyde and other 

 like bodies. Their observations were confirmed by Bach ^ who 

 worked on potato tubers. Anderson ** following the work of 

 Bach ft and of Haas and Hill %l on milk, found in twenty-three 



♦Kastle and Elvove : " Amer. Chem. Journ.," 1904, 31, 606; Priestley 

 and Armstead : " New Phyt.," 1922, 21, 62. 



t Thomas : " Science," 1927, 66, 115. 



+ Laurent : " Ann. Inst. Pasteur," 1890, 4, No. 11. 



§ Irving and Hankinson : " Biochem. Journ.," 1908, 3, 87. 



|| Loc. cit. H Bach : " Biochem. Zeit.," 1913, 52, 4 12 - 



** Loc. cit. ft Bach : loc. cit. 



XX Haas and Hill : " Biochem. Journ." 1923.. I7» 671. Also Haas and 

 Lee: id., 1924, 18, 614. 



