Regulation of gamma-aminobutyric acid degradation in Escherichia coli by nitrogen metabolism enzymes

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Abstract
The possible role of glutamate dehydrogenase, glutamate synthase and glutamine synthetase in the regulation of enzyme formation in the .gamma.-aminobutyric acid (GABA) catabolic pathway of E. coli K-12 was investigated. Evidence is presented indicating that glutamine synthetase acts as a positive regulator in the E. coli GABA control system. Mutations impairing glutamate synthase activity prevent the derepression of the enzymes of the GABA pathway in NH3-limited glucose media. Mutations resulting in constitutive synthesis of glutamine synthetase (GlnC) restore the ability of the glutamate synthase-less mutants to grow in glucose-GABA media and result in derepressed synthesis of the GABA enzymes. The loss of glutamate synthase activity probably affects the GABA control system indirectly by lowering glutamine synthetase levels.