CONTROL BY REPRESSION 



27 



effect is thought to result from tlie particular steady-state level of 

 arginiue produced b\- this organism under the test conditions. Fur- 

 ther repression is ol)tained upon addition of arginine to growing 

 cultures of strain W ( Vogel, 1953a ) . 



40 80 



TOTAL PROTEIN (Mg/mO 



20 



160 



Fig. 2-1. Repressed and derepressed formation of acetylornithinase in mutant 

 strain 39A-23R3 (circles) of Escherichia coli, and partially repressed formation 

 of the enzyme in wild-type strain W (triangles) of this species. Strain 39A-23R3 

 was grown, under anaerobic conditions at 37° C, on a glucose-salts medium, in 

 the presence of a supplement of L-arginine hydrochloride and N"-acetyl-L- 

 ornithine. The amount of (the preferentially utilized) arginine was such as to 

 support growth corresponding to a "total protein" value of 80 //g per ml of 

 culture. Acetylornithinase (per ml of culture) was determined after harvesting 

 of organisms and their disruption (in 0.1 M phosphate, pH 7, containing 1.0 mA/l 

 glutathione) with the aid of a Mullard Ultrasonic Disintegrator; the assay pro- 

 cedure and enzyme unit hove been described (Vogel and Bonner, 1956). Note 

 the abrupt change from repressed to derepressed synthesis at the beginning of 

 the (growth rate-limiting) utilization of acetylornithine. Strain W was cultivated 

 on unsupplemented glucose-salts medium and studied in the same general man- 

 ner as was the mutant strain. 



