ATTEMPTS TO ISOLATE PURE ENZYMES. 313 



unorganised ferments are typically found in the secretions of specialised 

 cells of the higher plants and animals, and take an important part in 

 the chemical changes involved in their nutrition. 



There is probably at bottom very little difference in the manner of action 

 of cellular ferments and enzymes. From the cell substances of several 

 bacteria, extracts have been obtained possessing the same fermentative action 

 as the living bacteria ; this indicates that in such bacteria, substances are 

 present in the cell which act like ordinary unorganised ferments, but normally 

 remain during the life of the cell within its substance, and perform their 

 fermentative functions there. 



A good example of such an isolation of an unorganised from an organised 

 ferment, is afforded by that series of brilliant researches into the nature of 

 the action of the micro-organism, torula ureas, upon urine, which began with 

 the observation that the change into ammonium carbonate was not stopped by 

 the presence of carbolic acid in sufficient amount to paralyse the growth of 

 the micro-organism, 1 and ended in the extraction from the bacteria of 

 a soluble ferment, which converted urea into ammonia and carbonic acid, even 

 in the presence of chloroform, which effectually stops all bacterial action. 2 



In a similar manner, a soluble ferment, capable of inverting cane sugar, 

 can be extracted from yeast cells after they have been killed by the action of 

 alcohol or ether, 3 and from certain putrefactive bacteria unorganised ferments 

 have been obtained, possessing an action on proteids analogous to that of the 

 proteolytic ferment of the pancreatic juice. Such intracellular soluble ferments 

 have not been shown to exist in by far the greater number of organised ferments, 

 but if they do so exist the only remaining difference between organised and 

 unorganised ferments is that in the former the substance formed by the cell 

 remains in the cell substance, and does its work there, the products of its 

 action being poured forth as a kind of secretion or excretion, while in the 

 latter the ferment becomes separated from the cell in a secretion, and carries 

 out its work apart from the cell. 



Most of the chemical changes involved in the digestion of the food 

 are brought about by the presence in the digestive secretions of soluble 

 ferments. So that digestion might be described as the physical and chemical 

 alteration of the foodstuffs, into forms letter fitted for absorption, ~by the 

 action of certain soluble ferments, the digestive enzymes. 



Attempts to isolate pure enzymes. Many attempts have been 

 made to isolate chemically pure enzymes, but the task is very difficult, 

 and it is highly probable that no one has yet succeeded in obtaining a 

 pure product. 



There are two great difficulties in the way : first, our ignorance of a 

 specific precipitant for any of the enzymes ; and, secondly, the extremely 

 small quantities in which they are present in the secretions. On account 

 of the first, the enzyme cannot be thrown out of solution unaccompanied 

 by other substances; on account of the second, it is not present in 

 workable quantity, and is rapidly lost in any lengthened process of 

 chemical manipulation. When to these disadvantages are added the 

 non-diffusibility of the enzymes, which shuts out a means of separating 

 them from the traces of proteid which always accompany them, and 

 their sensitiveness to reaction and temperature, some idea is obtained of 

 the difficulties which the problem of isolation presents. 



1 Hoppe-Seyler, Med.-chem. Untersuch., Berlin, 1871, Heft 4, S. 570. 



a Sheridan Lea, Journ. PhysioL, Cambridge and London, 1885, vol. vi. p. 136. 



3 Hoppe-Seyler, Ber. d. dcutsch. chem. Gesellsch., Berlin, 1871, S. 810. 



