Chemical Structure

Glutamine is a five-carbon compound with two nitrogen groups (Figure 14.1), is a relatively ubiquitous amino acid, and is unstable in the liquid phase. Glutamine is an amide derivative of the acid amino acid, glutamic acid (or glutamate). The conversion of glutamate to glutamine can occur in key tissues such as liver, brain, kidney, skeletal muscle, and intestine and is catalyzed by the enzyme glutamine synthase.12

Glutamine is a neutral polar amino acid, with an amine functional group, which is highly polar, and is capable of forming strong hydrogen bonds. This nature of the side chain enables glutamine to contribute to the stability of the protein molecule. The hydrogen bonding capacity of the amine group also enables interaction with water, making glutamine a highly hydrophilic amino acid.12

Glutamine is degraded to a-ketoglutarate, which is an important intermediate in several metabolic pathways, such as the citric acid cycle and the transamination process.12 Glutamine can also be converted to glutamate by the enzyme glutaminase, and thus plays an important role in the transamination process, in the synthesis of several key proteins, as precursors of other nonessential amino acids, and in the synthesis of excitatory neurotransmitters. Figure 14.2 summarizes the metabolism of glutamine.

Glutamine Protein Synthesis, etc. NH3-^ ^_^NH3^Urea, Nucleotide Synthesis, etc.

Glutamate Protein, Glutathione Synthesis, etc.

a-Ketoglutarate

Transamination Citric Acid Cycle

Non-essential Amino Acid Glucose Synthesis, Energy Production

Synthesis

FIGURE 14.2 Brief overview of glutamine metabolism.

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