Pyrimidines are heterocyclic six-membered nitrogen-containing carbon ring structures with uracil cytosine and thymine being the basal structures of ribose-containing nucleosides (uridine cytidine and thymidine respectively) or deoxyribose-containing deoxynucleosides and their corresponding ribonucleotides or deoxyribonucleotides.

CFP10 (71-85)

Homocitrulline is a metabolite that can be detected in larger amounts in the urine of individuals with urea cycle disorders. The accumulation of carbamyl phosphate due to a depleted supply of ornithine for the urea cycle may be responsible for the enhanced synthesis of homocitrulline and homoarginine in some cases.