Inhibition of synthesis of enzyme synthesis even in the presence of appropriate inducers. Catabolite Repression is best understood part of these controls. Each subunit can bind one cAMP, and when cAMP is bound, the protein binds to DNA at specific sequences, where it serves as a positive control element. Controls ability to utilize lactose, galactose, arabinose, maltose, tryptophan, D-serine, and histidine. EnzIIA Glu becomes phosphorylated as glucose supply runs out.
System is very important.
The regulation of enzyme levels, etc. must optimize the cell metabolism in ways that are still not understood completely. Mutant discovered in the 1950's could not reduce the rate of rRNA and tRNA synthesis. Mutants show lags of hours when down-shifted nutritionally. Wild-type adapts often in minutes. These compounds can be synthesized in two ways.