326 



CELL HEREDITY 



10 



30 40 50 60 

 Bacterial Protein (^g) 



70 



90 



FIGURE 11.10. The differential rate of synthesis of an induced enzyme. The kinetics of 

 formation of /iJ-galactosidase in E. coli are revealed by plotting enzyme activity against 

 total bacterial protein over a suitable time period. When inducer is added, enzyme 

 formation begins before the first measurement is made, and continues at a rate which is 

 a constant fraction of total protein synthesis in the growing population. When inducer 

 is removed, enzyme synthesis ceases and the molecules present are diluted out among 

 the multiplying cells (from Monod, 1958, Recueil des travaux chimiques des Pays-Bas, 

 77:569). 



small amount of basal enzyme present in uninduced cells, induction has 

 been viewed as the increased production over the basal level of an en- 

 zyme which the cell already knows how to make. 



A related finding of importance has come from studies of induced 

 synthesis of penicillinase in Bacillus cereus. The number of bound 

 penicillin molecules which serve as inducers of penicillinase has been 

 estimated by the use of radioactive penicillin, to be in the range of 

 100 molecules per cell c)r less. Since penicillina.se induction leads to the 

 presence of some 25,000 molecules per cell, it is evident that the role 

 of the inducer is a catalytic one with respect to enzyme formation. 



It now becomes relevant to look more directlv into the process of 

 enzyme formation itself, bv examining its kinetics. The curves in Figure 

 11.8 show a greater than linear increase in enzyme activity over time. 



