CHEMICAL COMPOSITION OF PLANTS 63 



As a result of the investigations by Willstatter and his col- 

 leagues, it has been possible during the past few years to under- 

 stand somewhat more clearly the chemical nature of enzymes. 

 Willstatter has based his work largely on the method of selective 

 adsorption of enzymes by certain finely ground substances, such 

 as clay and kaolin. Owing to their extremely high adsorptive 

 capacity, enzymes are removed from solutions more readily by 

 these substances than proteins, resins, or other colloids. By 

 repeated dissolving and adsorption, it is possible in this manner 

 to concentrate certain enzymes and to purify them from various 

 admixtures. The best results are secured with invertase from 

 yeast, which may be extracted in a quite pure condition by water. 

 Willstatter was able to increase the concentration of this enzyme 

 1,600 times. He has shown that such an almost pure preparation 

 of invertase does not contain phosphorus and does not give a 

 reaction for proteins or carbohydrates. But after all, a prepa- 

 ration of this type is not absolutely pure, and an analysis of it 

 does not give a true idea of its chemical nature. 



Purified enzymes are unstable, and under usual conditions 

 the molecules of enzymes are nearly always adsorbed on colloidal 

 particles. Willstatter has given these particles the name of 

 ''colloidal carriers." A considerable part of the physicochemical 

 pecuharities of solutions of enzymes is determined by the prop- 

 erties of the carriers. Complete separation of the enzyme and 

 its carrier is difficult to attain, and the numerous contradictions 

 and enormous accumulated literature about enzymes may be 

 explained by the fact that investigators studied the properties 

 not so much of enzymes as of their colloidal carriers. A number 

 of enzymes have now been ol^tained in crystalline form by 

 Semper, Northrop, and others. These seem to be the pure 

 substances free from admixture. 



Because it is not possible to isolate certain enzymes in a com- 

 pletely pure state, it is not possible to measure them quanti- 

 tatively. The fact of their presence is established by their 

 activity, and their amount by the quantity of substances trans- 

 formed per unit of time. However, even in applying crude 

 unpurified preparations of enzymes, one of their most interesting 

 properties was ascertained, viz., their capacity of transformmg 

 enormous amounts of organic substances, even when the enzyme 

 is taken in the minutest quantities. This property is still more 



