EFFECT OF ^H DURING GROWTH 



73 



substrates are toxic to the organism. Fig. 3 shows the 

 variation of the formation of alcohol dehydrogenase of Esch. 

 coli with growth jpH. The potential activity is that activity 

 estimated at the optimal activity pH (8-0) of the enzyme 

 and represents the total formation of enzyme within the cell , 

 the effective activity is the activity estimated at the _pH of the 

 environment in which the cell was grown. 



(c) A THIRD GROUP is formed by those enzymes whose 

 formation is maximal when the growth joH approximates to the 



90H 



Qm8 



60 H 



GROWTH 

 ;jH=9 



GROWTH 



4-5 5 6 1 



pW OF MEDIUM DURING GROWTH 

 (a) 



45 5 6 7 



REACTION joH 

 (b) 



Fig. 3. (a) Variation of potential activity (•— •) and effective 

 activity (x - - - x) of alcohol dehydrogenase of Esch. coli with 

 _pH of medium during growth. 

 (6) Variation with reaction ^H of activity of alcohol dehydrogenase 

 of Esch. coli grown at various pH values — showing that jjH of 

 optimum activity does not vary with growth 7>H. Qmb = M^- 

 methylene blue reduced/hr./mg. dry weight of organism. 

 (After Gale and Epps, Biochem. J., 1942, 36, p. 609.) 



value of their ^^H of optimum activity. It is remarkable 

 that, as far as we know, there is no enzyme whose formation 

 is not affected in some way or other by the environmental ^H 

 during growth. Enzymes of this third group, having functions 

 neither neutralising nor protective, are formed to a significant 

 extent over a hmited range of growth pH values centred about 

 the value of the optimal activity pH. The growth pH value 

 giving maximal formation is not necessarily the same as the 

 optimum activity ^H, as can be seen in Fig. 4 for the case of 



