The Glutamate Family of Amino Acids and Nitrogen Fixation

The Glutamate Family of Amino Acids and Nitrogen Fixation 

The conversion of ammonia into the a-amino group of glutamate and into the amide group of glutamine. The direct amination of a-ketoglutarate by NH4+ occurs only under conditions of high NH4+ concentrations, which are rarely found in nature. 

The structure of glutamine synthase from Salmonella typhimurium. The enzyme consists of twelve identical subunits arranged like a hexagonal prism, (a) View down the sixfold axis of symmetry. The top ring of monomers are alternately colored light and dark blue and the bottom ring of monomers light and dark red. The active sites of each monomer are marked by pairs of Mn + ions (white spheres). 

Glutamate serves as the starting material for the synthesis of glutamine, proline, and arginine (see fig. 21.1). Appropriately, these four amino acids are described as belonging to the glutamate family. In fungi, lysine is also included in this family (see fig. 21.1). 

In this section we discuss the pathways for glutamate and glutamine synthesis. We also discuss some other aspects of the nitrogen cycle. Consideration of the arginine pathway is deferred until the next chapter. 

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