160 AGEICULTTJEAL AND INDUSTEIAL BACTEEIOLOGY 



in a compound until the new compound formed is in 

 equilibrium with the unchanged compound. In other words, 

 enzymes not only can tear down, they are not only analytic, 

 but they are synthetic as well, being capable of building up 

 complex compounds from the simpler. For example, the 

 enzyme maltase, when brought in contact with maltose in 

 solution in water, changes most of this maltose into glucose. 

 Finally an equilibrium is established, there being present a 

 small amount of maltose and a large proportion of glucose. 

 Conversely when maltase is placed in a solution containing 

 glucose it will build up a small amount of maltose (iso- 

 maltose) until again the solutions are in equilibrium. 

 Undoubtedly in the body and in the cells of plants and 

 animals this synthetic action is quite as important as the 

 analytic. 



For convenience in study the enzymes may be divided 

 into three principal groups. The first includes those whose 

 function, from the standpoint of the cell, is primarily 

 digestive. These enzymes, for the most part at least, act 

 by a process of hydrolysis, that is, one or more molecules of 

 water are incorporated into the molecule which is to be 

 changed, which then breaks down into two or more simpler 

 molecules. Most of the extracellular enzymes are of this 

 nature. They are collectively known as hydrolases. The 

 second group includes those enzymes that bring about 

 changes primarily oxidative in nature. The changes which 

 they bring about usually yield energy to the cell. They may, in 

 a sense, be termed the respiratory enzymes. In some cases they 

 function by the addition of atmospheric oxygen or oxygen 

 derived from other compounds easily reduced to the com- 

 pound, usually a carbon compound, to be changed. Such 

 enzymes are generally termed the oxidases. Others bring 

 about a rearrangement of atoms within the molecule, an 

 intramolecular oxidation, and the molecule splits into two 

 or more new molecules. Such enzymes are frequently 



