80 



THE FORMATION OF ENZYMES IN Bx\CTERIA 



harvested at different ages of culture we find that {a) cells 

 harvested very early in the growth period have neither 

 enzyme ; (6) cells harvested during the phase of linear growth 

 possess a very active hydrogenase but no acetoacetic 

 decarboxylase ; and (c) cells harvested at the time of cessation 

 of growth have no hydrogenase activity but a very active 

 acetoacetic decarboxylase. These differences in time of 

 formation can probably be correlated with the fact that the 

 ^H of optimum activity of hydrogenase is 8-0, while that of 

 acetoacetic acid decarboxylase is approximately 5, and the 



ct>>- 



NUMBERS 



TIME OF GROWTH &» 



Fig. 7. 



joH of the medium falls from 7 to ca. 4-5 during the growth 

 period. 



It might be thought that some changes in the chemical 

 composition of the cell during its growth should be demon- 

 strable in view of the marked alterations in enzymic constitu- 

 tion. Changes in enzymic constitution involve changes in 

 protein constitution, but these may relate to the organisation 

 of the amino-acids within the molecules, rather than to gross 

 changes in their proportions. However, in recent years, 

 workers in Sweden have applied the technique of ultra-violet 

 spectrophotography to bacteria and have found very significant 

 changes in the composition of the cell during growth. Sub- 

 stances containing purines'and pyrimidines, such as nucleotides 



