Effects of Bacterial Growth on the Environment 183 



blood cells; an enterotoxin which affects the gastrointestinal 

 tract; a lethal toxin, which kills rabbits; and a skin-destroying 

 poison, called a dermonecrotizing toxin. Perhaps some, or all, 

 of these reactions are caused bv a single toxin manifesting itself 

 in different ways on diverse substances. 



ENZYMES 



The life of every cell depends upon chemical reactions activated 

 by organic catalysts called enzymes. The word enzyme comes 

 from the Greek and means "in leaven or in yeast." Chemists make 

 use of many inorganic catalysts to influence the speed of reactions, 

 but enzymes differ from these catalysts in having their origin only 

 within living cells and in being organic. 



Minute amounts of enzymes can catalyze the activity of a great 

 deal of substrate— the name applied to the material upon which the 

 enzyme acts. In fact, the catalyst can act upon substrate one 

 million times heavier than the enzvme without the latter beins[ used 

 up in the reaction. Chemically, enzymes are proteins, or proteins 

 attached to lower molecular weight substances. 



Naming of enzymes, with some exceptions, is done bv adding 

 the suffix "ase" to the specific substrate. For example, the enzyme 

 which attacks gelatin is termed gelatinase, and enzymes acting 

 upon protein are designated as proteases, or proteinases. En- 

 zymes may also be designated on the basis of types of chemical 

 reactions which they catalyze— oxidases, for example. 



The same factors that influence chemical reactions will aftect 

 enzyme activity, and these include temperature, pH, moisture, con- 

 centration of reacting substances, the presence of certain ions which 

 may stimulate or inhibit enzyme activity, etc. 



Living cells may produce two general classifications of enzvmes: 

 INTRACELLULAR and EXTRACELLULAR. Thcsc latter catalysts are 

 secreted, or excreted, through the cell wall, and thev prepare food 

 in the surrounding area for passage through the cell membrane. 

 Once the food substance gets within the cell, the intracellular 

 enzymes act upon it and prepare it for metabolism by the cell. 



The field of enzymology is a complex study, involving complex 



