Uridines

Uridines are nucleosides consisting of the pyrimidine base uracil linked to a ribose sugar, producing uridine. In RNA, uridine is one of the four standard nucleosides, pairing with adenine in the molecule’s structure and function. Uridine also exists in phosphorylated forms, including uridine monophosphate (UMP), uridine diphosphate (UDP), and uridine triphosphate (UTP). These nucleotides act as substrates for RNA synthesis and as carriers in carbohydrate metabolism through UDP-sugars.

Biochemically, uridine can be synthesized de novo or regenerated via salvage pathways. In salvage, uridine kinase phosphorylates uridine to UMP, which can be further phosphorylated to UDP and UTP. Uridine can also be interconverted with uracil and ribose-1-phosphate by uridine phosphorylase, with uracil entering the pyrimidine salvage pathway through enzymes such as uracil phosphoribosyltransferase. De novo pyrimidine biosynthesis ultimately provides UTP, which is required for RNA polymerization and other cellular processes.

Physiological relevance includes participation in RNA production and in the generation of UDP-sugars used for glycosylation and other carbohydrate-related pathways. In humans, dietary uridine supplements are marketed and studied for potential effects on brain metabolism and function, often in combination with choline and omega-3 fatty acids; however, clinical evidence for cognitive benefits remains inconclusive. Uridine should be distinguished from deoxyuridine and thymidine, the latter two being nucleosides of DNA.