392 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



Pasteur, who posited the necessity of life for fermentation, was op- 

 posed by Liebig who, without clearly stating his ideas, was of the opinion that 

 there was something in the yeast cell which actually produced the fermenta- 

 tion. Traube, in 1858, clearly stated the position that the yeast cell contained 

 a soluble ferment to which the decomposition was due. On account of the 

 confusion of the terms it was suggested by Kiihne in 1878 that the soluble 

 ferment should be termed enzyme (from cv V//,T/, in yeast), which signifies 

 that something in yeast which causes the fermentation of sugar. 



Not until 1897 was it definitely shown by Buchner that yeast did contain 

 an enzyme which fermented sugar in the absence of the living cells, and later 

 it was shown that other cells and bacteria also contained soluble ferments. 

 The term enzyme is now used for the active agent in all cases, and the term 

 fermentation for the process of decomposition. In France the term 'dias- 

 tases ' is used as a general word for enzymes. 



Occurrence and Preparation. 



Enzymes are present in all living cells. They are either excreted 

 in the juices by definite cells or glands of the organism, e.g. by the 

 salivary glands, the pancreas, etc. : that is, they act normally outside 

 the cells which produce them (ectoenzymes) , or they are not excreted : 

 that is, they act inside the cell envelope (endoenzymes). 



For purposes of investigation in the former case the juices of the 

 glands, such as saliva and pancreatic juice, are collected. In the latter 

 case the enzymes are extracted from the cells in which they are 

 present ; the cells require to be ruptured so as to obtain their contents. 

 The glands producing the secretion may also be extracted to obtain 

 the enzyme. 



The cells are ruptured by the following methods : 



(1) By drying the cells at a low temperature at 20 to 30 and 

 sometimes subsequently warming the dried mass to 50 or 60. 



(2) By drying the cells by stirring up the tissue with alcohol or 

 acetone and pouring off the liquid after a short time of contact. 



The dried material is treated with water ; the aqueous solution is 

 filtered and precipitated with alcohol. 



(3) By autolysis in the presence of toluene or other antiseptics ; 

 the cells are either mixed with antiseptic, or the tissue is minced and 

 suspended in water containing toluene, etc. The enzymes in the cell 

 dissolve the cell membrane and pass into solution. 



(4) By mechanical disintegration ; ' the cells are ground in a 

 mortar with sand. The ground-up mass may be diluted with water, 

 or the liquid contents may be separated from the cell walls by hyd- 

 raulic pressure. 



This method was used by Buchner to show the presence of the en- 

 zyme in yeast which ferments sugar. The ground-up yeast cells which 

 formed a liquid mass, were mixed with siliceous earth to form a thick 

 paste. The thick paste was pressed in a powerful hydraulic press. 



