WHAT ARE ENZYMES? 



BY 



BENJAMIN HARROW 



The word enzyme comes from a Greek word meaning 

 "in yeast" (en, in; zyme, leaven). Perhaps the most ac- 

 ceptable definition in the light of recent scientific research 

 is to say that it is a substance showing the properties of a 

 catalyst and produced as a result of cellular activity. 



But what is a catalyst ? The reader will recall his first 

 very simple experiment in the preparation of oxygen. 

 Here the learned instructor tells the bewildered youth that 

 if you put a little potassium chlorate in a test tube and 

 heat this very strongly, a gas is evolved which is later 

 identified as oxygen. Now by merely adding a small 

 quantity of a dirty black-looking powder, called man- 

 ganese dioxide, to the potassium chlorate, the oxygen is 

 evolved much more rapidly and at a much lower tempera- 

 ture. But this is not all. A careful examination at the 

 end of the reaction shows that the manganese dioxide has 

 not changed in any way : we have the same substance, and 

 the same amount of substance, at the end of the reaction 

 as at the beginning. Many such substances are known to 

 chemists. They all have this peculiarity : that they acceler- 

 ate chemical reactions, and that a relatively small at times 

 insignificant quantity of the catalyst suffices to bring 

 about the chemical change. 



In cells we find substances of this type, but thus far 

 these cellular catalysts, unlike the manganese dioxide, and 

 like proteins, have never been produced outside of the cell. 



76 



