CARBOHYDRATES 63 



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. 



The suffixes "lytic" or "clastic" are frequently used to indi- 

 cate breaking down of the substrate. Many enzyme actions are 

 hydrolytic in character, and the enzymes concerned are classed 

 as sucroclastic, lipoclastic (or lipolytic), proteoclastic (or pro- 

 teolytic) according to the type of substance acted on. Other 

 types are desaminases, which remove the ammo group from 

 amino acids, carboxylases, which remove C0 2 from the carboxyl 

 group COOH, and coagulases, which coagulate proteins. 



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. 



The degree of specificity is truly remarkable, for, of two com- 

 pounds differing only in the slightest detail of stereochemical 

 structure or arrangement of groups, an enzyme frequently will 

 decompose one and leave the other untouched. This strengthens 

 Fischer's key-lock idea. The enzyme is probably taken up, or 

 adsorbed by the substrate and a slight difference in molecular 

 structure may interfere with this process. 



