BY JAMES M PRTRIE. 80& 



evidence that amino-acids and amides are decomposed by enzymes 

 setting free ammonia. All these facts suggest strongly that 

 ammonia is the form most easily utilised by chlorophyllous- 

 plants. 



Protein-Synthesis in the Plant. 



From these very simple forms of food-stuff in soil and air the 

 plant, by an expenditure of a vast amount of energy, is able to 

 construct many different compounds increasing in complexity till 

 at last the protein-molecule is synthesised. The actual nutrition 

 of the organism now really commences, and so, as Green has said, 

 the food on which plants really depend is as complex as that on 

 which animals live. We do not know exactly by what stages 

 the plant builds up its proteins, though we are quite familiar 

 with the different steps in the reverse or downward grade of 

 protein-decomposition. 



Proteins, metaproteins, proteoses, polypeptides (coupled amino- 

 acids), amino-acids, fatty acids and ammonia. Through this 

 series the protein-molecule breaks up into a number of simpler 

 bodies, and each of these into still smaller groups, and finally 

 into the amino-acids, about twenty of which have been isolated. 

 The latter readily lose ammonia, and there are left the fatty 

 acids, or more frequently the oxy-fatty acids. 



By precisely the same steps we believe the synthesis to take 

 place — that the plant has not only the power to form all the 

 different amino-acids and their amides, but also to link these 

 together into polypeptides and peptones, to condense these into 

 proteoses, and finally into proteins. 



It has been already indicated that the initial substances ex^st 

 in the plant, viz., the oxy-fatty acids formed from carbohydrates 

 and fats, but just how the amino-radicle (NH 2 ) enters into the 

 acid to form the amino-acid, still remains a mystery. Lang, (24) 

 in 1904, observed that amino-acids are denitrified in the body 

 with loss of ammonia, possibly by the action of an enzyme. It 

 is possible that the reverse also takes place under the influence of 

 the special enzyme. 



