MECHANISM OF CHEMICAL CHANGES 161 



termed the splitiing enzymes or zymases. Third, still other 

 enzymes are primarily concerned in reduction processes. It 

 is evident that wherever food material is built up from 

 simple inorganic substances that there must be reduction 

 taking place. The building up of sugar, for example, from 

 carbon dioxide and water implies the reduction of carbonic 

 acid (H2CO3) to formaldehyde (HCHO), and the poly- 

 merization of this product into sugar. Such enzymes are 

 reductases. 



The hydrolytic enzymes are both extracellular and intra- 

 cellular. Most of the oxidizing, splitting, and reducing 

 enzymes are intracellular. 



Prom the standpoint of agricultural or economic sig- 

 nificance, the hydrolytic and oxidizing enzymes are by far 

 the most important. The hydrolytic and oxidative enzymes 

 produced by microorganisms will therefore be discussed. 



The Hydrolytic Enzymes or Hydrolases. — The hydro- 

 lases, that is, the enzymes which bring about splitting of 

 organic compounds by the addition of water, are for con- 

 venience divided into three groups, the carbohydrases, the 

 proteases or amidases, and the esterases or lipases. The 

 first group, the carbohydrases, bring about hydrolytic 

 decomposition of carbohydrates and related compounds. 

 The proteases hydrolyze the proteins and their various 

 decomposition products to amino acids. The esterases or 

 lipases hydrolyze the esters and particularly the glycerine 

 esters or fats. Enzymes belonging to all of the groups are 

 known among microorganisms. 



Cariohydrases. — Enzymes capable of hydrolyzing the 

 various complex carbohydrates down to the simple sugars 

 are known. The principal sub-groups of carbohydrases are 

 the cytases and cellulases which attack the celluloses and 

 hemicelluloses, the pectinases attacking pectin, the diastases 

 and inulases attacking starch and inulin, and the invertases, 

 which hydrolyze the disaecharides to simple sugars. 



