Localisation of Glutamine Synthetase in Chloroplasts

Abstract

Glutamine is of considerable importance in plants, as a readily metabolised and translocated intermediate, and as a product of ammonia detoxification. Glutamine synthetase carries out the ATP-driven addition of ammonia to glutamate to produce the amide. The source of ATP, and information on the metabolic role, for glutamine synthetase may be suggested by determining the location of this enzyme within the cell. Earlier work¹ suggested that glutamine synthetase was located in mitochondria, although later investigation² did not confirm this. We have found considerable amounts of glutamine synthetase in leaf tissues³, and recent results now suggest that a considerable proportion of the enzyme is associated with the plastid fraction of the cell.