MECHANISM OF METABOLISM 215 



The vinegar oxidase is an enzyme which remains in the cell of the 

 acetic bacterium, oxidizing alcohol to acetic acid. Its independence of 

 the living cell has been demonstrated by killing the cells with acetone. 



The PROTEOLYTIC ENDO-ENZYMES of yeasts, only, have been studied 

 extensively. That such enzymes exist is recognized by the observa- 

 tion that certain microorganisms do not liquefy the gelatin until 

 after they are dead and the proteolytic enzymes diffuse out through 

 the deteriorating cell membranes. That yeast in the absence of 

 sugar loses in weight, and that leucin and other cleavage-products of 

 protein are formed, was the first indication of a proteolytic process in 

 the yeast cells. By pressing the juice out of the ground yeast cells, 

 a liquid is obtained which liquefies gelatin, digests casein, albumin and 

 fibrin. The living yeast cell does not attack these compounds, be- 

 cause they cannot diffuse into the cell and the enzyme cannot diffuse 

 out. The proteolytic endo-enzyme of yeast is called endo-tryptase. 

 Its object is apparently the regulation of the protein-content of the cell 

 and perhaps it has some bearing on the formation of cell plasma. 

 The possible relation between enzymes and growth is discussed in a 

 following sub-chapter. 



If yeast is mixed with a weak antiseptic (chloroform, toluol) 

 the proteolytic process takes place quite rapidly. This process is 

 called autolysis (self-digestion). Similar autolytic enzymes are found 

 in other microorganisms. Autolysis is a well-known process in the 

 higher animals. To this is due the ripening of meat. 



Proteolytic endo-enzymes must be expected in all microorganisms 

 which depend upon protein as food material only. These organisms 

 will secrete certain enzymes which decompose the insoluble protein 

 into bodies which diffuse easily into the cell. Here, proteolytic endo- 

 enzymes further decompose these products. Such an endo-enzyme is 

 the amidase discovered by Shibata in the mycelium of Aspergillus 

 niger which forms ammonia from urea, acetamid, oxamid, biuret. 

 Endo-erepsin and amidase were also found in Penicittium camemberti 

 by Dox. 



Similar to these proteolytic enzymes is the urease which is formed 

 in large quantities in the so-called urea bacteria, but it is also present 

 in the mycelium of some molds. An endo-enzyme, splitting hippuric 

 acid into benzoic acid and glycocoll, is found in the mycelium of a few 

 molds. 



