against glutamine synthetase of the unicellular cyanobacterium
Synechocystis sp. strain PCC 6803 immunoreacted with glutamine
synthetase from the N2-fixing heterotrophic bacterium
Azotobacter chroococcum. In Western-blotting experiments this
antibody recognized a single protein of a molecular mass of
59 kDa corresponding to glutamine synthetase subunit. This
protein was in vivo-labelled in response to addition of ammonium,
both [3H]adenine and H332PO4 preincubation of the cells being
equally effective. Nevertheless, the amount of glutamine
available nitrogen source. Modified, inactive glutamine
synthetase was re-activated by treatment with snake-venom
phosphodiesterase but not by alkaline phosphatase. LMethionine-DL-sulphoximine,
an inhibitor of glutamine
synthetase, prevented the enzyme from being covalently modified.
We conclude that, in A. chroococcum, glutamine synthetase is
adenylylated in response to ammonium and that for the
modification to take place ammonium must be metabolized
