66 



THE POEMATION OF ENZYMES IN BACTERIA 



enzyme may further depend upon the presence of the substrate. 

 The mechanism of adaptation may be that the gene controls 

 the formation of an inactive enzyme-precursor which is only 

 activated by the presence of the substrate; alternatively, it 

 may be that the enzyme is formed in the presence of the gene 

 but is itself unstable in the absence of its substrate. 



SELECTION 



+ = present 



- = absent 



during 



growth 



ADAPTATION 



Fig. 1. Diagram to illustrate the difference between adaptation and 

 selection processes in enzyme formation. 



The presence of substances other than the substrate 



Adaptation involves a relation between the organism, the 

 enzyme, and the substrate, but sometimes substances other 

 than the specific substrate may play a part in the formation 

 or activity of an enzyme. The most marked example of this 

 is found when fermentable carbohydrate is added to the 

 medium. This problem has been studied chiefly with respect 

 to the effect of the presence of glucose during growth on the 

 production of enzymes concerned in the breakdown of proteins 



