Jean E. Brenchley

Glutamine synthetase as a regulator of enzyme synthesis.

Publisher Summary This chapter reviews glutamine synthetase as a regulator of enzyme synthesis. Glutamine synthetase stimulates the synthesis of enzymes responsible for the degradation of amino acids to glutamate; it inhibits the synthesis of glutamate dehydrogenase; and it may be involved in the inhibition of its own synthesis by ammonia and glutamine. The physiological significance of these regulatory activities of glutamine synthetase derives from its role in the synthesis of glutamate from ammonia. Glutamine synthetase may be an example of a protein that, in addition to its enzymatic function, can act as a repressor of its own synthesis. Such a double role may not be uncommon in the regulation of the synthesis of enzymes responsible for the biosynthesis of amino acids. Glutamine synthetase appears to have a more diverse and general role. In its adenylylated state or when charged with ammonia, it may repress glutamine synthetase; in its unadenylylated state or when not charged with ammonia, instead it represses glutamate dehydrogenase.