ENERGY SUPPLY OF THE CELL 37 



cells are dead in a fairly old culture (at least three days at 30-35°C.) 

 and that the enzyme which is quite stable leaves the dead cells, but 

 not the living ones. 



The proof that this fermentation can be used as the 

 only source of vital energy by the urea bacteria, has 

 been given by Sohngen (1909). 



Alcoholase. — Much more interest was displayed when 

 Buchner (1897) finally proved that alcoholic fermentation 

 could be separated from the living yeast cell. The old 

 famous dispute between Liebig and Pasteur had not 

 been forgotten and the discovery of the yeast-zymase, or 

 alcoholase, was a great step forward in biochemistry. 



Buchner obtained the zymase by tearing the cell walls 

 of the yeast cells through grinding with quartz sand, 

 and by pressing the ground yeast + quartz under high 

 pressures. Thus he obtained the cell sap of the yeast, 

 and this had retained the power of producing alcoholic 

 fermentation. Even after filtration through porcelain, 

 it was still able to bring about the formation of alcohol 

 and carbon dioxide from sugar. 



Later, another method was used more commonly. 

 The yeast was treated with alcohol and ether, or with 

 acetone; this killed the cells, i.e. it destroyed definitely 

 the power of yeast to grow and multiply, but not the 

 power to ferment. 



Lactacidase. — After the establishment of the enzy- 

 matic nature of the alcoholic fermentation, it was natural 

 that the same technique was applied to other fermenta- 

 tions as well. Herzog (1903) was the first to grind the 

 cells of Bad. acidi lactici Hueppe, and to obtain a cell 

 sap which would change lactose to lactic acid. This 

 was confirmed later by Buchner and Meisenheimer (1903) 

 who worked with Lact. Delbrilcki. 



