Evidence for adenylylation/deadenylylation control of the glutamine synthetases of Rhodospirillum tenue and Rhodocyclus purpureus.

The phylogenetically related phototrophic bacteria Rhodospirillum tenue and Rhodocyclus purpureus modulate activity of their glutamine synthetases by adenylylation/deadenylylation. Evidence for covalent modification includes the inhibitory effect of Mg on the activity of glutamine synthetase extracted from cells of either species grown on excess ammonia, and the lack of Mg inhibition of activity of the enzyme isolated from N-( R. tenue) or glutamine ( R. purpureus)-grown cells. In addition, snake venom phosphodiesterase treatment of glutamine synthetase from either species grown on excess ammonia relieved Mg inhibition of the enzyme (as measured via the γ-glutamyl transferase assay), and changed the cation specificity from Mn to Mg (in the biosynthetic assay). [ABSTRACT FROM AUTHOR]