ENZYMES 53 



Some enzymes are specific proteins requiring neither coenzymes nor 

 metals for activity. These enzymes must contain as an integral part of 

 their structure the specific groups whereby they react with the substrate. 

 Other enzymes consist of two moieties, a specific protein and a specific 

 nonprotein compound which can be detached from the protein. In the 

 process of purifying an enzyme by dialysis the activity may be lost and 

 later restored by adding to the dialyzed material some boiled juice from 

 the tissue under investigation. These specific nonprotein compounds are 

 known as coenzymes. Neither the specific protein nor the coenzyme alone 

 functions as the enzyme; both are required for activity. The specific 

 protein is called the apoenzyme, while the combination of apoenzyme and 

 coenzyme is called the holoenzyme. Still other holoenzymes consist of an 

 apoenzyme, a coenzyme, and a metallic ion. Coenzymes, being non- 

 protein in nature, have proved to be more easily isolated and studied than 

 the specific protein moieties of enzymes. Coenzymes are a varied group 

 of compounds, some relatively simple in structure and others more com- 

 plex. The vitamins are known to enter into the structure of some 

 coenzymes, and it is supposed it is through such coenzyme molecules that 

 the vitamins exert their specific effects. The same coenzyme may com- 

 bine with many specific proteins to form different enzymes. 



FACTORS AFFECTING ENZYME ACTIVITY 



Some of the factors influencing enzyme activity affect the intact organ- 

 ism as well as isolated enzyme systems. While the situation within the 

 intact organism is more complex, a knowledge of the behavior of isolated 

 systems will be useful in interpreting the behavior of living fungi. The 

 factors which will be discussed are temperature, hydrogen-ion concentra- 

 tion (pH), chemical reagents (activators and inhibitors), and radiation. 



Temperature. The rate of many reactions is approximately doubled 

 for each 10°C. increase in temperature. The rate of reactions catalyzed 

 by enzymes also increases with temperature. This increase is not main- 

 tained indefinitely, for enzymes are destroyed by temperatures of less 

 than 100°C. Although there are some reports in the literature of the rate 

 of enzymatic reactions being increased as much as fivefold by a 10°C. 

 increase in temperature, for most enzymatic reactions the increase in rate 

 is less than twofold. This increase between two temperatures 10°C. 

 apart is called the temperature coefficient, or Qio. Since the increase in 

 rate is not exactly constant, it is desirable to specify the temperatures 

 involved; e.g., Q20-30. 



A reaction with a Qio of 2 proceeds sixteen times faster at 40°C. than 

 at 0°C. Or, the transformation of a given amount of substrate which 

 requires 16 hr. at 0°C. will occur within 1 hr. at 40°C. Figure 9 shows the 

 theoretical effect of temperature upon the amount of substrate trans- 



