72 



THE FORMATION OF ENZYMES IN BACTERIA 



investigation of the amount of enzyme formed in the cell at 

 various growth ^H values shows a direct relation between 

 the formation of the neutralising mechanism, suppression of 

 the non-neutralising mechanisms, and the ;pH of the environ- 

 ment (see Fig. 2). 



(6) Protective mechanisms: the function of some 

 enzymes such as catalase is to destroy metabolites which, 

 if allowed to accumulate, would prove toxic to the cell. All 

 enzymes are optimally active at a definite ^H and, conse- 

 quently, as the environment pH diverges from this pH of 



o 



X 



< 60- 



r- 



> 



•^ 40- 



-100^ 



80° 

 < 



pH OF MEDIUM DURING GROWTH 

 Fig. 2. Variation of formation of glutamic acid decarboxylase 

 and deaminase of Esch. coli with the pB. of the medium 

 during growth. 



optimal activity, the effectiveness of each enzyme unit 

 decreases. This means that in the case of catalase, which 

 has optimal activity at ^H 6-5, the enzyme unit is considerably 

 less effective during growth occurring at pH 9 than at pH 6-5. 

 In such cases we sometimes find that the organism compensates 

 for this loss of efficiency per enzyme unit by the production of 

 more enzyme so that the effective activity (= No. of enzyme 

 units X activity of each unit at the environmental pH) is 

 roughly constant whatever the pB. in the medium. Enzymes 

 whose formation is affected by pH in this way are urease, 

 catalase, formic, and alcohol dehydrogenases — enzymes whose 



