138 NUTRITION AND METABOLISM. 



sively substituted by the more significant word lipase. Occasionally they 

 are called lipolytic enzymes which expression is analogous to the proteo- 

 lytic enzymes; in the same way, the term amylolytic enzyme is used for 

 diastase. 



ENZYMES OF PROTEINS. The enzymes decomposing protein bodies, 

 generally called proteolytic enzymes or proteases, have been known for 

 nearly a century. Though the difficulty of analyzing protein bodies 

 accurately prevents an absolute knowledge of proteolysis, much effort has 

 been made to become acquainted with the very important group of en- 

 zymes which accomplish the digestion of protein food. Naturally, 

 most experimenting has been conducted with pepsin and trypsin of the 

 animal body, accordingly these are better understood than others, and 

 only little work has been done with microbial enzymes; but there is so far 

 as can be determined little appreciable difference between the proteolytic 

 enzymes obtained from different organisms, whether low or high in the 

 plant or animal world, consequently many experiences 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. 

 Mavrojannis tested for the intensity of gelatin decomposition with 

 formaldehyde. The peptones of gelatin will solidify with formaldehyde 

 while amino-acids are not affected. 



Proteolytic enzymes were first divided in to two groups: pepsins, which 

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

 alkaline media. The names are derived from pepsin (peptase), the pro- 

 teolytic enzyme of the animal stomach, and from trypsin (tryptase) which 

 is found in the small intestine of animals. This classification 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 trypsin 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 



