CARBOHYDRATES 47 



ending "ase" is now employed to indicate that a substance is 

 an enzyme, and the remainder of the word usually indicates 

 either the substance upon which the enzyme acts, the nature of 

 the reaction it brings about, or some other property of the com- 

 pound. The substance upon which the enzyme acts is called 

 the substrate. The classification of the enzymes is only pro- 

 visional until a better one is possible. They are grouped accord- 

 ing to the substances acted upon, or the character of the reac- 

 tion induced, thus there are proteases (act on proteins), lipases 

 (act on fats), amylases (act on starch and amylum), lactase 

 (on lactose), maltase (on maltose), oxidases, reductases, etc. 

 Of the older names we have pepsin, rennin, trypsin, zymase 

 (found in yeast), etc. 



Specific Nature. As may be inferred from the above state- 

 ments, the enzymes act only upon particular substances or 

 classes of substances, and in general an enzyme which acts upon 

 one compound will not act upon any other. The enzymes are 

 thus said to be specific in their action, that is, each one acts 

 only on a particular kind of material, or brings about one parti- 

 cular kind of chemical action. Emil Fischer, one of the most 

 brilliant chemists of all times, has likened this characteristic to 

 the fitting of a key with its lock. As a matter of fact, the en- 

 zymes are believed to fit onto the substances they act upon, form- 

 ing temporary compounds which quickly break down again. 



Influence of Temperature. One of the characteristics of the 

 enzymes is their extreme sensitiveness to temperature. The 

 temperature of the .solution in which an enzyme is acting will 

 be found to influence greatly the speed of the action. The tem- 

 perature at which different enzymes will act best is known as 

 their optimum temperature, and for the enzymes in the body 

 this is in the neighborhood of 37-40 C., in other words about 

 body temperature. The enzymes in some of the cold-blooded 

 animals, however, whose body temperature varies with that of 

 their surroundings, act well at temperatures much lower than 

 this, and it is obvious that enzymes in plant cells must work well 

 at temperatures much below that of the body. If a solution 

 containing an enzyme is heated to 60 -80 the enzyme is de- 



