EFFECT OF CARBOHYDRATE 67 



and amino -acids, but the effect is by no means restricted to 

 these enzymes alone. If we study the formation of a deaminase 

 such as alanine deaminase, which carries out the reaction 



Alanine 



CH3 . CHNH2 . COOH + > CH3 . CO . COOH + NH3, 



deaminase 

 in Esch. coli which has been grown in an amino-acid mixture 

 with and without glucose, we find that the amount of deaminase 

 produced in the absence of glucose is some twenty times 

 greater than that produced in its presence. No really satis- 

 factory explanation of this effect has yet been put forward. 

 At one time it was suggested that the inhibitory action of the 

 presence of glucose on the formation of some enzymes could 

 be attributed to the production of fermentation acids, but in 

 many cases this has now been disproved. A further suggestion 

 that has been put forward is that the presence of glucose 

 during growth has a " protein sparing " action similar to that 

 postulated in mammalian nutrition. The addition of glucose to 

 washed suspensions of Esch. coli has no effect on the deaminase 

 activities of the cells, so that glucose has no effect once the 

 enzymes have been formed in the cell and the inhibitory 

 action must affect enzyme formation during growth. 



An alteration of the _pH of the medium during growth does 

 have a marked effect on enzyme production, but the suppres- 

 sion of deaminase formation, for instance, by the presence of 

 glucose is greater than can be explained by the fall in ^H 

 due to acid formed by its fermentation. Table VI shows 

 the action of the presence of glucose during growth on the 

 formation of various enzymes of Esch. coli, and it can be seen 

 that in some cases the effect can be satisfactorily explained 

 by fermentation acidity, while in others the effect is greater 

 than, or sometimes even opposed to, that produced by an 

 equivalent acidity during growth. Only in the case of 

 glucozymase (the enzyme system responsible for the first 

 stage of glucose fermentation) does the presence of glucose 

 during growth result in an enhanced activity over and above 

 that due to acidity. 



