Effect of glutamine on glutamine-synthetase regulation in the green alga Monoraphidium braunii

Glutamine-synthetase (GS; EC 6.3.1.2) activity and protein levels were measured in crude extracts from Monoraphidium braunii Naegeli, strain 202-7d, cultures grown under different nitrogen sources. Only ammonium and L-glutamine promoted a partial enzyme inactivation, which, in the case of L-glutamin...

Full description

Saved in:
Bibliographic Details
Published inPlanta Vol. 195; no. 3; pp. 434 - 439
Main Authors Garcia-Fernandez, J.M, Lopez-Ruiz, A, Alhama, J, Roldan, J.M, Dapena, J.D
Format Journal Article
LanguageEnglish
Published 1995
Subjects
ammonium compounds
assimilation
Chlorophycota
enzyme activity
glutamate-ammonia ligase
glutamine
inactivation
methionine sulfoxamine
nitrogen
nitrogen metabolism
protein content
sources
Online AccessGet more information

Cover

More Information
Summary:Glutamine-synthetase (GS; EC 6.3.1.2) activity and protein levels were measured in crude extracts from Monoraphidium braunii Naegeli, strain 202-7d, cultures grown under different nitrogen sources. Only ammonium and L-glutamine promoted a partial enzyme inactivation, which, in the case of L-glutamine, was accompanied by a significant repression of GS. Methionine sulfoximine (MSX), a strong inhibitor of GS, produced a drastic inactivation of GS which was concomitant with a marked increase in GS protein as measured by rocket immunoelectrophoresis. Such an increase was prevented in the presence of cycloheximide. The effect of the L-glutamine analog on GS activity and protein was partially inhibited if L-glutamine was also added to cell cultures, possibly indicating competition in the transport of these two substances. In addition, the effects of MSX were reversed after longer times when cultures were treated with smaller concentrations of inhibitor. Treatment of cell cultures with azaserine, a specific inhibitor of glutamate synthase, the second enzyme acting in the ammonium assimilation pathway, promoted a strong GS inactivation and a partial repression of this enzyme, which paralleled a specific increase in the intracellular pools of glutamine High-performance liquid chromatography measurements of intracellular amino-acid concentrations showed that glutamine levels correlated negatively with GS concentration. A role for glutamine as a negative effector of GS synthesis is proposed.
ISSN:0032-0935
1432-2048
DOI:10.1007/BF00202602