CHAPTER III 



ENZYME ACTION 



Some indication has been given in the previous chapter of the large 

 number of complex processes which take place in the plant, and it has 

 been mentioned that many of these are controlled by enzymes. 



The most remarkable feature in connexion with the chemical pro- 

 cesses of plant metabolism is the ease and rapidity with which, at 

 ordinary temperatures, chemical reactions take place, when under artificial 

 conditions they need a much longer time and higher temperatures. 



It has been found that many of the chemical reactions in the plant 

 can be brought about in vitro on addition of certain substances which 

 can be extracted from the plant. These substances are known as enzymes. 

 It is the property 'of enzymes that they are able to accelerate reactions 

 which, in their absence, would only take place very slowly. The enzyme 

 cannot initiate these reactions and does not form part of their final 

 products. 



Some inorganic substances have the same property of accelerating 

 reactions, and such substances are termed catalysts. For example, when 

 water is added to ethyl acetate, the latter begins to be decomposed slowl}^ 

 into ethyl alcohol and acetic acid : 



ethyl acetate + water — ^ ethyl alcohol -I- acetic acid, 



but if, in addition, some hydrochloric acid is added, hydrolysis takes place 

 with much gi-eater rapidity, and at the end of the reaction the hydrochloric 

 acid is found unchanged. Hence in this case hydrochloric acid is an 

 inorganic catalyst. Many other similar instances are known as, for 

 example, the catalyzing effect of a small (juantity of manganese 

 dioxide which brings about the liberation of oxygen from potassium 

 chlorate at a much lower temperature than by heat alone. 



By analogy, therefore, an enzyme may be defined as an organic 

 catalyst produced by the plant. 



Another point in connexion with the above-mentioned reaction of 

 water with ethyl acetate, is the fact of its being representative of the 

 type known as reversible. After a certain amount of acetic acid and 

 ethyl alcohol has been formed, these recombine to form ethyl acetate 

 until in time a certain point of equilibrium is leached. Since the same 

 o. 2 



