PROTEOLYTIC ENZYMES OF SOIL FUNGI 



527 



The small quantity of substratum decomposed by the safranin 

 precipitate might be merely due to the fact that some of the 

 enzyme was carried down mechanically by the safranin precipi- 

 tate, and not in the form of a salt such as the color-base safranin 

 is supposed to form with the acid-like trypsin. The filtrates 

 from the safranin precipitate were weaker in their enzymatic 

 action than the normal solution obtained by filtering the original 

 culture of the organism. This may be due to several reasons: 

 first, the filtrate from the safranin precipitate was slightly di- 

 luted by the addition of the safranin solution; second, some of 

 the enz5rme might have been carried down by the precipitate; 

 and third, the safranin itself may have had some injurious effect 

 upon the enzyme. There does not seem to be any doubt that 



TABLE 11 

 The action of safranin as a precipitating agent for the exoenzymes of A.niger 



the enzymes of many microorganisms can attack true proteins. 

 What, then, is the true nature of the enzymes? They cannot be 

 similar to the animal trypsins, because they act best in a neu- 

 tral and even slightly acid medium, are not precipitated by 

 safranin, and act best at lower temperatures. They cannot be 

 pepsins alone, because they decompose peptones and the splitting 

 of casein and other proteins goes further than the peptone stage. 

 The only thing that could be suggested is that these enzymes 

 should not be classified with the animal proteolytic enzymes at 

 all. If anything, they approach nearer the plant enzymes and 

 they are either tryptases similar to the animal trypsins, but dif- 

 ferentiated from them by certain characteristics; or they are a 



