78 BACTERIAL METABOLISM 



VI. QUALITATIVE INFLUENCE OF UTILIZABLE CARBOHYDRATES 

 UPON THE ELABORATION OF PROTEOLYTIC ENZYMES. 



Certain bacteria, as for example B. proteus, characteristically pro- 

 duce proteolytic enzymes which rapidly dissolve gelatin by hydrolytic 

 cleavage. These enzymes are exo-enzymes; that is, they may be 

 obtained sterile and free from bacteria simply by passing gelatin 

 liquefied by their action through sterile unglazed procelain filters. 

 Although the bacteria which elaborated the enzymes are removed by 

 this filtration, the sterile filtrate still contains the active enzyme which 

 will liquefy considerable amounts of gelatin. The function of these 

 enzymes is to prepare the gelatin for assimilation by the proteus bacil- 

 lus: the gelatin is broken down by enzyme action to gelatin peptone 

 or even to polypeptids. The proteus bacillus does not produce soluble 

 gelatin-splitting enzymes in gelatin containing utilizable carbohy- 

 drate, although sugar-free gelatin contains them in considerable 

 amounts. These gelatinases, however, will liquefy sugar-gelatin quite 

 as readily as sugar-free gelatin, indicating that the enzyme itself 

 is not inactivated by the sugar, at least in the amount usually 

 employed, 1 per cent. The same phenomenon is observed in cul- 

 tures of the cholera vibrio and many other bacteria which liquefy 

 sugar-free gelatin. Extensive investigations by Auerbach, 1 and by 

 Kendall, Day and Walker 2 have shown that the gelatinase, which, 

 as has been noted, is produced only in sugar-free gelatin, although 

 it liquefies sterile sugar gelatin, prepares protein for utilization by 

 these bacteria for purely catabolic purposes; if the organisms have 

 access to utilizable carbohydrate the enzyme is not produced by 

 them, because they utilize the sugar, not the protein, under these 

 conditions as the source of their energy. These observations indicate 

 how fundamentally the metabolism of bacteria is influenced by the 

 nature and composition of the substrate upon which they are grown. 



VH. QUANTITATIVE MEASURE OF BACTERIAL METABOLISM. 



It is possible to measure the nitrogen metabolism of bacteria under 

 varying conditions with a very considerable degree of accuracy in 

 spite of the minute amounts of products involved. Such measure- 

 ments are not only indicative of the nature and degree of the decom- 



1 Arch. f. Hyg., 1897, xxxi, 311. 



2 Jour. Am. Chem. Assn., 1914, xxxvi, 1962. 



