ENZYMES AS SYNTHETIC AGENTS 483 



For the sake of clearness these four questions will be con- 

 sidered separately, though obviously they are all sub-divisions 

 of the one general problem of constructive nitrogen metabolism 

 in the organism. 



1. The First Inclusion of Nitrogen 



There is now a very general consensus of opinion that the 

 nitrogen absorbed by a green plant through its roots may have 

 been presented to it in various forms, the most suitable being 

 nitrates, though ammonium compounds may readily be utilised. 1 



The greater value of nitrates to the plant may be due to the 

 fact that in the reduction of these compounds energy may be 

 liberated that can be utilised in synthetic processes. Thus the 

 agricultural chemist is familiar with the fact that the employ- 

 ment of nitrate as a manure is followed by accelerated vegetative 

 growth ; and there is considerable evidence that energy supplied 

 in the form of nitrate may be in part utilised in the series of 

 katabolic changes connected with respiration and growth. 



The nitrate supplied to the plant has to be reduced, as in 

 the protein molecule it occurs in association with hydrogen. 

 The distribution of nitrates within the plant indicates that this 

 reduction usually occurs in the tissues of the leaf, as it is here 

 that the nitrates are found to disappear. If then enzymes are 

 employed in this reduction, they should be present in the leaf. 

 Enzymes with this power of reducing nitrate have been obtained 

 from plant tissues by some investigators, but they do not 

 represent the only possible agency for the reduction of nitrates. 



Bach has suggested that formaldehyde, so often reported as 

 present in leaves, might reduce the nitrate to hydroxylamine, 

 this subsequently giving rise to formaldoxime and ultimately to 

 formamide : 



H H 



I I 



CHO + NH..OH ^C:N.OH+H 2 



and 



H 



H 



I H 



C: N. OH -» I 



I CO.NH, 

 H 



Formaldoxime. Formamide. 



1 Hutchinson and Miller, "The Assimilation of Nitrogen by Higher Plants," 

 Journal of Agricultural Science > vol. iv. p. 282, 191 2. 



