CHAPTER XVI 

 ENZYMES 



Nor seed nor fruit have I, — 

 Nor loss nor gain nor change in me is found. 



— John Tabb. 



Catalyzers. — It has long been known by chemists that certain 

 reactions between two substances would go on more rapidly in 

 the presence of a third substance. Oxygen and hydrogen unite 

 with explosive violence in the presence of spongy platinum. In a 

 similar manner the breaking down of cane sugar, which takes 

 place very slowly in a neutral aqueous solution, is accelerated 

 greatly by the addition of a small amount of sulphuric or some 

 other mineral acid. 



Such accelerations have been called catalytic reactions, and the 

 process, catalysis, has been defined by Ostwald as "the accelera- 

 tion of a chemical change by the presence of some foreign sub- 

 stance." Such catalytic reactions are characterized in the follow- 

 ing ways : 



1. The catalyzer or catalytic agent (catalyst) does not appear 

 in the end products of the reaction. It is not appreciably altered 

 by the reaction and remains nearly the same in quantity and qual- 

 ity at the end of the reaction as at the beginning. 



2. The catalyst does not initiate reactions but merely changes 

 the rate at which the reaction would have continued without it. 

 The reactions cited above are reactions which go on slowly in the 

 absence of the catalytic agent but proceed at an increased rate 

 in its presence. 



3. The effect of the catalyzer is proportional to the amount 

 present, if the amount of material acted upon is much in excess 

 of the catalyzer, as is generally the case. 



4. In proportion to the amount of catalyzer used, the effect of 

 the reaction is very great. A very small amount of material is 

 able to bring about a very great change; this is to be expected 

 if the catalyzer can be used over and over again. Thus one gram 

 of invert ase may hydrolyze a million times its weight of cane 

 sugar in a comparatively short time. 



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