214 NUTRITION AND METABOLISM 



ZYMASES 



The zymases are the agents which furnish the energy for cell life 

 by causing fermentative decompositions. As has been stated before, 

 the processes which provide for energy must take place inside of the 

 cell. Consequently, all fermenting enzymes are endo-enzymes. The 

 difference between the soluble enzymes and the endo-enzymes is very 

 plainly shown in the following table, giving the energy liberated by 

 the various enzymes by acting upon i g. of substance. 



ENERGY LIBERATED FROM i G. OF SUBSTANCE 



Soluble Enzymes Endo-enzymes 



Pepsin, trypsin o calories Lactacidase 80 calories 



Lipase 4 calories Alcoholase 120 calories 



Maltase, invertase 10 calories Urease 230 calories 



Lactase 23 calories Vinegar-oxidase 2,500 calories 



The microbial cell does not lose much energy by the activity of 

 the soluble enzymes outside of the cell, because their energy yield is 

 insignificant. 



The first zymase known was urease, the enzyme which changes 

 urea to ammonium carbonate. The actual investigation of the 

 zymases did not start until Buchner had demonstrated that yeast can 

 be ground with infusorial earth until all cells are lacerated, and then 

 can be pressed and the juice filtered without losing the power of alco- 

 holic fermentation. Such fermentation cannot be due to anything 

 but a soluble compound of the yeast cell. Thus the alcoholase was dis- 

 covered. It was found later that yeast may be killed by alcohol, 

 ether or acetone without losing its fermenting power. 



This last method was applied later to lactic bacteria, and it was 

 proved that the lactic acid is also produced by an enzyme, lactaci- 

 dase. It is possible to kill the lactic bacteria so that they do not 

 multiply but. still continue to form acid. It seems quite probable 

 that other fermentations of carbohydrates, like the butyric and the 

 gassy fermentations, are really due to enzymes. It is very difficult 

 to give the experimental proof, however. These enzymes are so un- 

 stable that it requires much experience to separate them from the cell, 

 and it is also quite difficult to obtain bacteria in quantities large 

 enough for such experiments. 



