Automatic Adjustment in Bacterial Cells 315 



With catalase a more complex response to the fall in pH at 

 the end of the cycle was observed. As the cells entered the 

 stationary phase there was a very marked increase in the 

 catalase content, far greater than would have been needed 

 simply to compensate the lowered specific activity. If the 

 pH fall was prevented by alkali addition the rise in catalase 

 amount did not occur. The formation of the extra enzyme, 

 however, appears here to be stimulated not directly by the 

 adverse pH itself but by a factor (perhaps peroxide formation) 

 which comes into being concomitantly with the pH change. 

 This factor observably slows down growth, which now becomes 

 limited, in the extreme case, by the rate at which the catalase 

 system can be constituted to overcome the adverse circum- 

 stances. The enzyme activity per cell thus tends to rise 

 steeply. 



The behaviour of the dehydrogenases has some interesting 

 aspects. Glucose dehydrogenase maintains itself at a nearly 

 constant level throughout the growth cycle. Even when the 

 cells have been grown with succinate instead of glucose as the 

 sole source of carbon the glucose dehydrogenase still remains 

 throughout at about its normal level. The strain of bacteria 

 studied shows a very long lag on first being transferred to 

 a succinate medium. During this lag there is, contrary to 

 what might perhaps have been expected, no appreciable 

 increase in the succinic dehydrogenase, which, however, 

 increases very rapidly and markedly in amount as soon as 

 actual growth starts. On the other hand, during the lag there 

 is a considerable increase in deaminase activity. These 

 observations show that the adaptation to succinate is a fairly 

 complex process involving more than one enzyme. And 

 indeed it is not altogether surprising that a new reaction 

 pattern differing from the old in more than one respect has to 

 be established. The succinic dehydrogenase does not reach its 

 optimum value until several cycles in the succinate medium 

 have been completed. On the return to the glucose medium of 

 the succinate-adapted cells the succinic dehydrogenase falls 

 to its original level, but not so rapidly as simple dilution of the 



