Biochemical and Biophysical Phenomena 767 



approximately one-half, because each particle of enzyme repeats the 

 same type of work over and over. Enzymes are specific in their action, 

 each one causing a specific chemical change upon one substrate. Only 

 a small quantity of an enzyme is required to produce a specific reaction. 

 Many enzymes are produced in an inactive condition, known as pro- 

 enzymes, which are changed into an active condition by such activators 

 as acids, alkalis,, or electrolytes. The number of different enzymes pro- 

 duced by the protoplasm of even one cell is probably quite large because 

 the variety of reactions in such a cell is quite great. Enzymes are indis- 

 pensable for all metabolic activities. Only a few of the more common 

 enzymes with their functions will suffice to illustrate their general distri- 

 bution. The various stages in the process of food digestion are depend- 

 ent upon specific enzymes. The ripening and over-ripening of fruits are 

 due to specific enzymes. Autolytic enzymes normally present in animal 

 tissues sometimes cause the spoilage of meats in storage. Certain enzymes 

 are responsible for specific effects in the preparation of foods, such as 

 bread, butter, cheese, sauerkraut, etc. Industrially, enzymes are used in 

 manufacturing alcohol, acetic acid, and lactic acid, etc. Enzymes in the 

 liver change glucose into glycogen which is stored in the liver. Another 

 enzyme changes unusable glycogen into usuable glucose again. The 

 enzyme luciferase oxidizes luciferin, which is the photogenic material in 

 certain animals, such as the firefly. 



Plant and Animal Hormones, Including the Ductless (Endocrine) 

 Gland Secretions 



A hormone (Gr. hormao, to excite) is a chemical substance which in- 

 creases activity, while a chalone (Gr. chalinas, to curb) diminishes or re- 

 tards activity. Hormones differ from enzymes in that they take part in 

 the reaction and are consequently used up. In this case they must be 

 replaced. Hormones are produced in one part of the body and carried 

 to other parts of the body where they produce specific structural or 

 functional changes. Since these secretions do not travel in special ducts 

 to their ultimate destination, they are known as ductless gland secre- 

 tions. They are also known as endocrine secretions (Gr. endon, within; 

 krino, separate). They are summarized in the chapter on Biology of 

 Man. 



The activities and characteristics of animal hormones have been known 

 for some time, but only recently have data been secured for plant hor- 

 mones. Growth hormones in plants are normally found in all rapidly 



