Properties and regulation of glutamine synthetase from Rhodospirillum rubrum

Abstract

Glutamine synthetase from Rhodospirillum rubrum was purified and characterized with respect to its pH optimum and the effect of Mg2+ on its active and inactive forms. Both adenine and phosphorus were incorporated into the inactive form of the enzyme, indicating covalent modification by AMP. The modification could not be removed by phosphodiesterase. Evidence for regulation of the enzyme by oxidation was obtained. Extracts from oxygen-treated cells had lower specific activities than did extracts from cells treated anaerobically. Glutamine synthetase activity was found to decrease in the dark in phototrophically grown cells; activity was recovered on re-illumination.

The activity of adenylyltransferase in Rhodospirillum rubrum is only affected by α‐ketoglutarate and unmodified PII proteins, but not by glutamine, in vitro

“…Previous studies using wild-type R. rubrum extracts have shown that the covalent modification of GS is adenylylation [3,29] and that the reaction requires the presence of the GlnB protein [22]. Using purified components we have now confirmed and extended these results.…”

“…This regulation responds to both the nitrogen status and the energy ⁄ redox status of the cell, and it is reasonable to believe that the effectors in this regulation are related to the assimilatory reactions, especially as GS activity in R. rubrum is affected by the same 'switch-off' effectors, e.g. ammonium ions and change to darkness, as nitrogenase [1,3].Glutamine synthetase is one of the key enzymes in nitrogen metabolism and is strictly regulated in most bacteria [5]. In Escherichia coli, this regulation occurs at three levels: transcriptional, feedback inhibition and covalent reversible modification, all in response to the nitrogen status in the cell [6][7][8].…”

Purification of P II and P II -UMP and In Vitro Studies of Regulation of Glutamine Synthetase in Rhodospirillum rubrum

“…Among the anoxygenic photosynthetic bacteria, glutamine synthetase in R. rubrum has been most extensively characterized (6,20,25,32). Studies at the metabolic level have demonstrated that the enzyme is regulated in a way partly similar to that of the E. coli enzyme; however, several interesting differences have also been observed (6,20,25,32).…”

Evidence of covalent modification of glutamine synthetase in the purple sulfur bacteriumThiocapsa roseopersicina

“…Thus, the isoactivity point could not be defined. Previous studies revealed that GS from the purple nonsulfur bacterium Rhodospirillum rubrum also lacks an 'isoactivity point' [19], but nevertheless is regulated by adenylylation/ deadenylylation. Because of this, perhaps the R. rubrum and T. roseopersicina enzymes share major biochemical properties.…”