抄録
Catabolite repression of β-galactosidase synthesis in E. coli 3000A1 (adenine-) was studied under a variety of growth conditions. The differential rate of induced β-galactosidase synthesis was maximal at the growth rate of 0.75 division per h, irrespective of whether growth conditions were aerobic or anaerobic. The addition of cyclic AMP (CAMP) to the medium partly restored the repressed synthesis of β-galactosidase under some growth conditions, but showed little or no effect on the enzyme synthesis under other conditions. Although growth rate and profile of β-galactosidase synthesis in glucose-grown cells were similar to those in arabinosegrown cells, the acceleration of β-galactosidase synthesis upon the addition of cAMP was found only in glucose-grown cells. The cells aerobically grown in the presence of glycerol, xylose, or arabinose showed a high synthetic rate of cAMP and were insensitive to exogenously supplied cAMP as regards β-galactosidase synthesis. Although the cells grown with glucose showed similar rates of cAMP synthesis under aerobic and anaerobic conditions, the differential rate of β-galactosidase synthesis was much higher in the anaerobic state than in the aerobic state. These findings support the idea that catabolite repression found in the strain is caused through two mechanisms, i.e., cAMP-mediated and cAMP-independent ones.
