142 ORGANIC AGRICULTURAL CHEMISTRY 



Oxidizing Enzymes. — The enzymes causing oxidation re- 

 actions involve in most cases the presence of atmospheric 

 oxygen, though in many important cases the oxygen comes 

 from other compounds rich in oxygen, such as nitrates and car- 

 bohydrates. They are most important in the final oxidation 

 reactions in plants and animals by which the food is oxidized 

 in the cells of the organism and energy is liberated. The prin- 

 cipal substance thus oxidized in the animal body is glucose, 

 but it is possible that both fats and proteins are oxidized in 

 this same way. 



Reducing Enzymes. — The reducing enzymes produce the 

 reverse reaction to the above and are probably present in ani- 

 mal and plant organisms, but no common examples can be given. 



Coagulating Enzymes. — The chemical reaction involved in 

 the coagulation of proteins, e.g. the coagulation of milk casein, 

 has not been established. The coagulating enzymes are found 

 both in digestive fluids (milk coagulating) and in blood (blood 

 clotting) . 



Decomposing and Splitting Enzymes. — Those enzymes 

 which cause the decomposition of the molecule without ac- 

 companying extra molecular change of the preceding types 

 are of two classes, (i) Sugar (monosaccharose) fermenting 

 enzymes that decompose glucose or fructose and yield alcohol 

 and carbon dioxide. This is the action of the yeast enzyme 

 zymase. (2) Sugar-splitting enzymes that decompose a large 

 molecule into a smaller one with the same percentage com- 

 position, e.g. the conversion of glucose into lactic acid, 

 C6H12O6 —^ 2 CsHeOs- 



Character of Enzyme Action 



Specific Action of Enzymes. — It has been found that en- 

 zymes act specifically upon certain compounds and not upon 

 others. Emil Fischer believes that this specific action is due 

 to the stereochemical configuration of the molecules of both 

 the substance acted upon and the enzyme, i.e. that the enzyme 

 and compound are related in their configuration as a key is to 



