Azospirillum brasilense glutamine synthetase: influence of the activating metal ions on the enzyme properties

The kinetic properties of the Mg2+-activated and Mn2+-activated glutamine s ynthetase (GS) of Azospirillum brasilense in the biosynthetic reaction mere studied. The Mg2+-supported and Mn2+-supported GSs in an average state of adenylylation varied in pH optimum, maximum activity, saturation functions for ammonium and glutamate, affinity to substrates, and in the Me2+-ATP rat io required for the optimal enzyme activity. Seventeen other cations mere t ested for the maintenance of GS activity, The level of the latter and the k inetic behavior of the GS in A.brasilense is suggested to depend essentiall y on the concentrations of Mg2+, Mn2+ and Co2+, as well as on their ratio.