92 THE SYNTHESIS OF PROTEINS 



donator must be found ; from Eckerson's work and on theo- 

 retical grounds sugar is indicated, but Bernheim found that, 

 in vitro, both glucose and sucrose gave negative results. 

 To summarize these observations : there occur in a number of 

 plants a reducing mechanism, generic with aldehydase of animal 

 origin, capable of reducing nitrate to nitrite, provided an 

 hydrogen donator is present. There are, however, certain 

 difficulties to its unqualified acceptance as the mechanism used 

 by the plant in the first stage of protein synthesis : in vitro 

 the action is very slow at air temperature and in the absence 

 of acetaldehyde, but at higher temperatures (Anderson, 45 ; 

 Eckerson, 50 ; and Bernheim, 37 C.) the reaction is relatively 

 rapid, especially in the presence of acetaldehyde. Further, 

 in the test tube, the activity of the mechanism falls off in 

 time for a reason unknown, but this may not occur in the very 

 different conditions obtaining in an active plant cell. 



Photochemical. — The evidence in support of the thesis that 

 the reduction of nitrate to nitrite is a photochemical reduction 

 is not extensive. 



It was first shown by Thiele * that potassium nitrate, on 

 exposure to the rays from a quartz mercury vapour lamp, 

 was reduced to potassium nitrite with evolution of oxygen. 

 With a view to the further study of the photochemical decom- 

 position of nitrites, Baudisch f exposed mixtures of potassium 

 nitrite and methyl alcohol in aqueous solution to diffused 

 daylight and to ultra-violet light and found that the methyl 

 alcohol became oxidized to formaldehyde at the expense of 

 the nitrite which was reduced to hyponitrite, and this latter, 

 at its moment of formation, reacted with the formaldehyde 

 to produce the potassium salt of formhydroxamic acid — 



KN0 2 + CH a OH =- KNO + HCHO + H 2 

 KNO + HCHO = H . C . OH 



I! 



NOK 

 The reduction of nitrate or nitrite in the presence of alcohol is 



* Thiele : " Ber. deut. chem. Gesells.," 1907, 40, 4914. See also Moore 

 and Webster : " Proc. Roy. Soc.," P>, 1919, 90, 158. 



f Baudisch : " Ber. deut. chem. Gesells.," 191 1, 44, 1009. See also 

 loc. cit., 1916, 49, 1 176, and 1918, 51, 793. Baly, Hcilbron and Hudson, 

 " Journ. Chem. Soc," 1922, 121, 1078. 



