PROTEOLYTIC ENZYMES OF SOIL FUNGI 525 



microorganisms studied; the different enzymes behaved some- 

 what differently in this case, the largest amount of amino nitro- 

 gen being obtained from fibrin by the exoenzymes of P. chryso- 

 genum and by the endoenzymes of A. ochraceus. 



The digestion of fibrin and crystalline egg-albumen is shown 

 to be positive, hence the enzymes of the microorganisms cannot 

 be erepsins or only ereptic in nature; although it is possible that 

 other organisms behave in an entirely different way from those 

 studied in this paper. 



It still remained to find out whether the enzymes are tr5T)tic 

 in nature. Otsuka (1916) claimed that trypsin retains its activity 

 after filtration through a Chamberland filter, but erepsin becomes 

 inactive. The filtrate of a culture of A. niger grown for eight 

 days on the Peptone-Czapek solution was filtered through a no. 

 6 Pasteur-Chamberland filter, and both filtered and unfiltered 

 portions were compared with the untreated liquid as to their en- 

 zymatic power. The tests were performed in the ordinary way, 

 by adding 20 cc. of each fluid to 80 cc. of peptone and casein 

 solutions, so as to make them of 1 per cent concentration; 

 these were incubated for forty-eight hours at 37°C. and amino 

 nitrogen determined. 



As is seen from table 10, the filtering of the enzyme culture 

 through a porcelain filter results only in a very slight diminution 

 in the activity of the enzymes, which may be due to a mere 

 mechanical retention by certain colloidal particles of a small 

 quantity of the enzyme. If the results of Otsaka hold true for 

 erepsin, the enzymes of the microorganisms studied do not seem 

 to be erepsins. 



Robertson (1907) pointed out the fact that when a saturated 

 solution of safranin is added to a neutral or faintly alkaline so- 

 lution of trypsin, a flocculent precipitate is formed which con- 

 tains the most active constituents of the trypsin. When this 

 precipitate is added to a solution of a protein, the latter will be 

 decomposed very rapidly, while the filtrate left, after the safra- 

 nin-trjrpsin precipitate is removed, is almost inactive. This be- 

 havior of the safranin toward the trypsin in solution can be 

 utilized for the testing of the tryptic nature of the exoenzymes of 



