1188 ENZYMES OK SOLUBLE FERMENTS. 



The Enzymes ok Soluble Unorganized Ferments. 1 



In the chemistry of animal and vegetable cells it is found 

 that in many cases substances may be extracted from them which 

 possess to a most striking degree the property of inducing 

 change in an indefinitely large mass of certain other substances 

 without themselves undergoing any observable alteration. 

 These agents are known as the enzymes or soluble ferments, 

 and the essential conception of an enzyme is summed up in 

 the above statement of the most remarkable characteristic of 

 their activity. Further investigation of these enzymes shows 

 that their activity is dependent upon many subsidiary factors 

 which are more or less common to them all. Thus their activ- 

 ity is largely dependent upon temperature, being absent at 

 sufficiently low temperatures, increasing as the temperature 

 is raised to a certain optimal point which varies slightly for 

 different enzymes, then again diminishing as the temperature 

 is further raised and finally disappearing. By the action of a 

 sufficiently high temperature they permanently lose their char- 

 acteristic powers and are now spoken of as being 'killed.' 

 Again the enzymes are extremely sensitive to the reaction, 

 whether acid, alkaline or neutral, of the solutions in which 

 they are working, also to the presence or absence of various 

 salts, some of which merely inhibit their action while others 

 permanently destroy it; and their activity is in all cases les- 

 sened and finally stopped by the presence of an excess of the 

 products to whose formation they have given rise. It has been 

 already said that an enzyme may be killed by exposure to a 

 high temperature, but this only holds good when they are in 

 solution, or if in the solid form they are heated in a moist con 

 dition. When perfectly dry they may be heated to 100° — 160 

 without any permanent loss of their powers. It will be seen 

 that so far the enzymes have been characterized solely with 

 reference to the peculiarity of their mode of action and to the 

 influence of surrounding conditions upon that activity, and the 

 question of their probable chemical composition has been left 

 untouched. Notwithstanding the frequent endeavours which 

 have been made to prepare the enzymes in a pure condition, it 

 is unwise to lay any great stress upon the results of the analysis 

 of these so-called 'pure ferments,' bearing in mind that, as in 

 the case of the proteids, no criterion of their purity exists. 

 This much however may be said. In the majority of cases, an- 



1 It appears advisable to use the term ' enzyme ' to denote the soluble unor- 

 ganized ferments generally, reserving the older name of ' ferment ' for the 

 organized agents such as yeast to which it was first applied. If this be done it 

 will be convenient to use the expression 'zymolysis' to denote the changes pro- 

 duced by the enzymes in their action on other substances, and to apply the term 

 ' fermentation' to the action of the organized ferments. 



o 



