EVIDENCE OF COVALENT MODIFICATION OF GLUTAMINE-SYNTHETASE IN THE PURPLE SULFUR BACTERIUM THIOCAPSA-ROSEOPERSICINA

It was shown that glutamine synthetase of purple sulfur bacterium Thio capsa roseopersicina is regulated by covalent modification. This concl usion is made on the basis of results showing that: (i) incubation of cells under conditions of nitrogen deprivation in the light lead to an increase of glutamine synthetase activity; (ii) addition of ammonium to nitrogen-starved cell suspensions caused a rapid decrease of glutam ine synthetase activity; (iii) inhibition of glutamine synthetase by f eedback modifiers was higher in ammonium-treated cells than in those s tarved for a nitrogen source; (iv) treatment of purified glutamine syn thetase and cell-free extracts with phosphodiesterase was accompanied by an increase of glutamine synthetase activity, indicating the cleava ge of modifying residues covalently bound to glutamine synthetase mole cules.