Properties and regulation of glutamine synthetase from Rhodospirillum rubrum

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.