ENZYMES. FERMENTATION 



413 



THE CATALYTIC ACTION OF ENZYMES. 



The resemblance of the action of enzymes to that of inorganic catalysts 

 was pointed out by Berzelius. The agent producing the chemical change 

 apparently takes no part in the reaction and can at the end be recovered 

 unchanged. Minute quantities are capable of effecting a large amount of change ; 

 as an example may be quoted O'Sullivan and Tompson's statement that invertase 

 can hydrolyse 200,000 times its weight of cane sugar. 



The resemblance is most marked if the velocity of the action of enzymes 

 be compared with that of inorganic catalysts, as is shown in the curves in 

 Fig- 55- 



100 



75 



50 



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FIG. 55. From Bayliss's " Nature of Enzyme Action ". 



10 



Curve B is the velocity of the action of hydrochloric acid upon cane 

 sugar. Curve A is that of invertase upon cane sugar. Curve C is that of 

 trypsin upon caseinogen. This latter curve is the most typical of enzyme action, 

 that of invertase being more exceptional. 



The curve B is a logarithmic curve. The enzyme curves deviate from 

 this in two important particulars. They are linear at the commencement and 

 at the end. The cause of the deviation of the enzymic curve from that of a 

 proper catalytic curve has been found to be due to three causes : 



(1) Disappearance of the enzyme during the course of the action. Enzyme 

 solutions, as previously stated, are never pure ; they contain other substances 

 which act upon and remove or destroy the enzyme. 



(2) Effect of the products of the action ; they hinder the reaction. 



(3) Combination of the enzyme with the substrate which also takes an 

 appreciable time. 



The linear part of the curve is the result when either substrate is in excess 

 at the beginning, or enzyme in excess at the end. 



