HYDROLYSIS OF PROTEIN 93 



a purely photochemical reaction since no such change could 

 be produced in the dark even if the solutions were boiled. 



It will be observed that the evidence mainly relates to 

 ultra-violet radiation, in the absence of which the plant can 

 flourish and form proteins. For this reason, and especially in 

 view of the facts relating to the occurrence of nitrites and the 

 formation of proteins in the dark places of the plant, the con- 

 clusion is justified that in the plant the photochemical re- 

 duction of nitrate is without significance. 



Assuming that the reduction of nitrate is the beginning of 

 protein synthesis, the further sequence of reactions is a matter 

 of speculation. If the doctrine of the reversibility of enzyme 

 action be held, as it generally, if not always is, the reversal of 

 the changes effected by the plant, by means of its enzyme 

 mechanisms, in the dissociation of the protein molecule, may 

 throw light on the formation of proteins ; for this reason these 

 changes may first be considered. 



HYDROLYSIS OF PROTEIN. 



The protein content of a seed or other storage organ, 

 whether temporary, as the leaf, or more permanent, is a 

 reserve food which must be hydrolysed before it can be trans- 

 located and made available for the growing parts. The cleav- 

 age products of proteins yield a large number of amino acids 

 (Vol. I., p. 443) and a number of amides. The following amino 

 acids have been identified in the plant : arginine, glycine, 

 histidine, leucine, lysine, phenyl alanine, tryptophane, and 

 tyrosine. Of the amides, asparagine and glutamine are im- 

 portant members, from the point of view of plant physiology, 

 and of these asparagine is the more conspicuous. 



This dissociation of protein takes place with some degree 

 of rapidity ; Jodidi * found that after eight days' germination 

 in darkness, 48 per cent, of the proteins originally present in the 

 fruit of the maize was hydrolysed to water-soluble diffusible 

 compounds. The evidence of his analyses indicate that pro- 

 teoses and polypeptides are amongst the first degradation 



* Jodidi : " J. Agric. Res.," 1925. 3*> IT 49- 



