Homocitrulline is an amino acid found in mammalian metabolism as a free-form metabolite of ornithine (another amino acid not found in proteins but is involved in the urea cycle).
Through the process of carbamylation, homocitrulline amino acid residues can also be formed in proteins. Carbamylation results from the binding of isocyanic acid with amino groups (isocyanic acid spontaneously derived from high concentrations of urea) and primarily leads to the formation of either N-terminally carbamylated proteins and/or carbamylated lysine side chains (forming homocitrulline residues).
It is known that elevated urea directly induces the formation of potentially atherogenic carbamylated LDL (cLDL). High blood concentrations of urea leading to the carbamylation process were detected in uremic patients and patients with end-stage renal disease. Homocitrulline can be detected in larger amounts in the urine of individuals with urea cycle disorders.
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