CHAPTER VIII 



ENZYMES AND ENZYMATIC ACTION 



Enzymes and Fermentation 



In the discussion of alcohol and its formation from glucose 

 sugar by the process of fermentation we referred to the sub- 

 stances known as enzymes and to the particular enzyme, zymase, 

 which produces alcoholic fermentation. The action of enzymes 

 or of bacteria, the latter owing their activity to the enzymes 

 produced, have also been mentioned in connection with acetic 

 acid, lactic acid, glucose, fructose, sucrose, starch, fats and pro- 

 teins. It will thus be seen that enzymes play an important 

 part in the natural formation of many organic substances. In 

 fact, most of the chemical changes occurring in plants and 

 animals are produced by enzymes. This important connection 

 with living things makes it desirable, before we take up the 

 chemistry of plant and animal physiology, to discuss briefly the 

 general facts in regard to enzymes. 



The term fermentation applies to those chemical reactions 

 which take place usually in connection with living organisms, 

 in which the organism or substance produced by it takes no 

 real part in the mass changes of the compounds involved. 

 They act by their mere presence, or, as we say, catalytically^ 

 the chemical reaction itself being one of the ordinary type, 

 such as oxidation, hydrolysis, etc. 



The word enzyme means in yeast, and signifies the fact that 

 the activity of yeast is due to an enzyme or enzymes. The 

 isolation of the enzyme in yeast was not accomplished, however, 

 until the word had been suggested and used for some time. 

 The first enzymes known were those found in the digestive 



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