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Glutamine is converted to glutamate by glutaminase, or several other enzymes, by the removal of the amide nitrogen. Proline is first converted to a Schiff base and then converted by hydrolysis to glutamate-5-semialdehyde. All of these changes occur on the same carbon. Arginine and histidine contain 5 adjacent carbons and a sixth carbon attached through a nitrogen atom. The catabolism of these amino acids is thus slightly more complicated than glutamine or proline. Arginine is converted to ornithine and urea. Ornithine is further transaminated to produce glutamate-5-semialdehyde. Glutamate-5-semialdehyde is converted to glutamate. Tetrahydrofolate is the cofactor in the final step converting histidine to glutamate. Transamination or deamination of glutamate produces a-ketoglutarate which feeds into the citric acid cycle. (This definition may be outdated - see the DesignNote.)
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