212 NUTRITION AND METABOLISM 



ences with animal pepsin and trypsin can be applied to microbial 

 enzymes. 



The specific chemical action of these enzymes is referable to hydro- 

 lysis; the large protein molecule is broken up into smaller molecules 

 by addition of water. Various proteolytic enzymes differ in the extent 

 of decomposition. While some, like pepsin, produce mainly peptones, 

 trypsin is able to split protein to amino-acids and even to ammonia. 

 Mavrojann is tested for the intensity of gelatin decomposition with 

 formaldehyde. The peptones of gelatin will solidify with formalde- 

 hyde while amino-acids are not affected. 



Proteolytic enzymes were first divided into two groups: pepsins, 



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which act best in slightly acid solutions, and trypsins, which act best 

 in slightly alkaline media. The names are derived from pepsin (peptase) 

 the proteolytic enzyme of the animal stomach, and from trypsin (tryp- 

 tase) which is found in the small intestine of animals. This classifi- 

 cation cannot be used for the enzymes of microorganisms because 

 there is no definite line established by the acidity. Some enzymes 

 work in either acid or alkaline media equally well, preferring a neutral 

 reaction. Enzymes should be classified according to the substances 

 they act upon or perhaps according to the nature of the products 

 resulting from the fermentation. This would bring pepsin and tryp- 

 sin into one class, both acting upon protein bodies as such; they, 

 however, differ in the intensity of action as shown by their products, 

 the pepsin forming mainly peptones, the trypsin carrying on the 

 decomposition as far as amino-acids and traces of ammonia. Another 

 class recently recognized is ereptase (erepsin) which cannot decom- 

 pose protein, but readily attacks peptones, decomposing them much 

 in the same way as trypsin. Pepsin, trypsin and erepsin do not 

 break up amino-compounds. 



The presence of proteolytic enzymes in microorganisms is readily 

 tested by cultivation on nutrient gelatin. The proteolytic enzyme 

 secreted by the cells will liquefy the gelatin. Generally, an organism 

 that liquefies the gelatin will also decompose the casein of milk and the 

 protein of blood serum. There are some exceptions, however, as is 

 shown in the following table, after Frost and McCampbell. A + 

 sign means proteolysis, a sign means no action, 



