336 B. Magasanik, et al. 



led us to conclude that this effect is a manifestation of 

 enzyme repression (Neidhardt and Magasanik, 1956a, 1957; 

 Magasanik, 1957; Magasanik, Neidhardt and Levin, 1958). 

 Glucose is metabolized much more rapidly than other carbon 

 compounds and it was postulated that the products of its 

 degradation are formed faster than they can be removed by 

 the anabolic reactions of the cell. Glucose inhibits the forma- 

 tion of an enzyme only when the ultimate product of the 

 action of the enzyme is a metabolic intermediate which is also 

 readily produced by the degradation of glucose. The congruity 

 of this phenomenon with that of enzyme repression is clear: 

 the formation of the enzyme is inhibited by the ultimate 

 product of its action. 



This concept of the "glucose effect" is supported by the 

 results of an investigation of glucose metabolism in A. 

 aerogenes.* During growth in a medium containing mineral 

 salts, ammonium sulphate and glucose, the organism excretes 

 a variety of degradation products of glucose, including 

 pyruvate, gluconate, and 2-ketogluconate, into the culture 

 fluid ; after exhaustion of the glucose the cells continue to grow 

 on these degradation products at a diminished rate. Cells 

 harvested during exponential growth on glucose and sus- 

 pended in phosphate buffer, oxidize glucose and gluconic acid 

 rapidly, but oxidize pyruvate very slowly; cells harvested 

 after they have exhausted the glucose and entered the 

 stationary phase, oxidize all three substrates rapidly. Cells 

 grown on glycerol, whether harvested during or after the 

 exponential phase of growth, oxidize glucose and pyruvate 

 rapidly, but oxidize gluconate slowly (Table I). Glucose- 

 grown cells, suspended in the mineral salts medium from 

 which ammonium sulphate has been omitted, oxidize glucose 

 much more rapidly than when suspended in phosphate 

 buffer; this stimulation of glucose metabolism was found to 

 be due to the Mg2+ which the medium contains. Interestingly 



* The experimental work described in this section was carried out by one of 

 us (A.K.M.) at the Children's Cancer Research Foundation and was supported 

 by U.S. Public Health Service Grants C-1691 and CY-3335. 



