THE MECHANISM OF ORGANIC SYNTHESIS m 



As an intermediate product in the synthesis of starch, glyoxylic acid 



| has been described as occurring in the green parts of plants. This 



COOH 



substance with ammonia gives formyl glycine, and by the splitting off of 

 formic acid, glycine or amino-acetic acid. Why nitrates are necessary for 

 certain forms of plants is not at present understood. In the proteins nitrogen 

 always occurs in an unoxidised form as NH or NH 2 , and the nitrates taken 

 up from the soil must therefore undergo reduction before they can be built 

 into the protein molecule. It is supposed that they may pass through a series 

 of reductions, namely : 



HN0 3 HN0 2 HNO H 2 N-OH 



nitric acid nitrous acid hype-nitrous acid hydroxylamino 



and that the latter substance then reacts with formaldehyde or other sub- 

 stance derived from the carbon dioxide assimilation to form amino-com- 

 pounds. In general we may say that the probable mechanism of formation 

 of amino-acids is the production of a-oxyacids, which then react with 

 ammonia to form the amino-acids of the protein molecule ; but of the 

 exact steps in this process we are at present ignorant. Knoop's work would 

 point to the ketonic acids as forming one step, and as interacting with 

 ammonia, with simultaneous reduction, to form amino-acids. 



The pyrrol ring which occurs in proline and in oxyproline may possibly 

 be derived from an open chain amino-acid, and it has, in fact, been suggested 

 that the proline found in the products of the acid digestion of proteins is 

 derived from ornithine by a process of condensation with the loss of ammonia. 

 Thus: 



CH 2 NH 2 .CH 2 .CH 2 .CH.NH 2 COOH becomes 

 CH 2 .CH 2 .CH 2 .CH.COOH 



NH 



or, as it is generally written : 



CH 2 CH 2 



CH CH.COOH 



2 



NH 



Its pie-existence in the protein molecule is, however, practically assured, and 

 it plays an important part in the building up both of chlorophyll and 

 hsematin, the prosthetic group of haemoglobin. 



CH-NH 



Iminazol || y CH 



CH N 



occurs in histidine (which is iminazol alanine), and can be formed fairly 

 readily by the action of certain catalytic agents on a mixture of 3 

 ammonia. Thus, if a solution of glucose with ammonia and ; 



