No evidence of covalent modification of glutamine synthetase in the thermophilic phototropic bacterium Chloroflexus aurantiacus

Abstract Regulation of glutamine synthetase (GS) in the thermophilic green phototrophic bacterium, Chloroflexus aurantiacus , was studied. The enzyme was partially purified from cells grown photosynthetically in media with limiting (1 mM) or non-limiting (10 mM) NH⁺₄-concentrations. GS preparations from both cell types were indistinguishable in respect to pH-optimum of GS-transferase activity, sensitivity to feedback modifiers (AMP, L-alanine, glycine) and lack of Mg-inhibition of transferase activity. In contrast to results obtained with a GS preparation from the facultatively phototrophic bacterium, Rhodopseudomonas sphaeroides , the catalytic properties of Chloroflexus GS did not change during incubation with snake venom phosphodiesterase suggesting the absence of in vivo regulation of Chloroflexus GS by adenylylation/deadenylylation.