Regulation of transcription and activity of Rhizobium etli glutaminase A.
The present study determines the regulatory mechanisms that operate on Rhizobium etli glutaminase A. glsA gene expression levels were evaluated under several metabolic conditions by fusions of the glsA gene promoter and the transcriptional reporter cassette uidA2-aad. glsA expression was directly correlated to the glutaminase A activity found under the tested growth conditions, reaching its maximum level in the presence of glutamine and during exponential growth phase. Glutamine induces glsA expression. The influence of allosteric metabolites on glutaminase A activity was also determined. The purified enzyme was inhibited by 2-oxoglutarate and pyruvate, whereas oxaloacetate and glyoxylate modulate it positively. Glutaminase A is not inhibited by glutamate and is activated by ammonium. Glutaminase A participates in an ATP-consuming cycle where glutamine is continually degraded and resynthesized by glutamine synthetase (GS). GS and glutaminase A activities appear simultaneously during bacterial growth under different metabolic conditions and their control mechanisms are not reciprocal. Slight overproduction in glutaminase A expression causes a reduction in growth yield and a dramatic decrease in bacterial growth. We propose a model for regulation of glutaminase A, and discuss its contribution to glutamine cycle regulation.
Huerta-Saquero
Alejandro
A
Departamento de Biología Molecular y Biotecnología, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, Apdo. Postal 70228, México D.F. 04510, Mexico.
Calderón-Flores
Arturo
A
Díaz-Villaseñor
Andrea
A
Du Pont
Gisela
G
Durán
Socorro
S
D000494:Allosteric Regulation; D001483:Base Sequence; D017931:DNA Primers; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D005972:Glutaminase / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000502:physiology; D042163:Rhizobium etli / Q000201:enzymology*; D014158:Transcription, Genetic / Q000502:physiology*
D017931:DNA Primers; D004791:Enzyme Inhibitors; D005972:Glutaminase