Arginine

Route: Glutamate + Acetyl-CoA → N-Acetylglutamate → N-Acetylglutamyl phosphate → N-Acetylglutamate 5-semialdehyde + Glutamate → N-Acetylornithine + α-KG → Ornithine + Carbamoyl phosphate → Citrulline + Aspartate → Argininosuccinate → Arginine + Fumarate

The first step puts an acetyl group on the amino group of glutamate. The acetyl group stays on while the side chain is activated with ATP and reduced to an aldehyde, as in the proline pathway. A transaminase then moves an amino group from a second glutamate onto the aldehyde, and the cap is removed with water to give ornithine. Some organisms hand the acetyl group straight to a new glutamate instead of releasing acetate; the deacetylation shown is the variant that releases acetate. Ornithine then goes through the same three reactions as in the urea cycle (carbamoyl phosphate, aspartate, release of fumarate) and ends as arginine. Humans do not use this route. Citrulline made in the intestine is converted to arginine by the kidneys. Arginine is conditionally essential.

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Steps

Enzyme names and EC numbers are those used on the interactive board. Checked against sources: see the claim table in the repository (tools/pathway_data/checks).