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Glutamine
Synthase -
E.coli glutamine synthetase has a MW of 600,000. It consists of 12 identical subunits, each of MW 50,000. The subunits are arranged in the form of two hexagonal rings of six subunits each, with a spacing of 4.5 nm between them. Cations of Mg ++ and Mn ++ are required for stability.
The enzymatic activity of GS is regulated by three different mechanisms:
(i) Variation in the concentration of divalent cations results in inter conversion of GS between a relaxed (inactive) and a taut (active) form.
(ii) The enzyme is covalently altered by reversible adenylylation of a specific tyrosyl residue on each subunit.
(iii) Feedback inhibition by various end products of glutamine metabolism.
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