Orotidine5monophosphate

Orotidine-5'-monophosphate (OMP), also known as orotate monophosphate, is a nucleotide that functions as an intermediate in de novo pyrimidine biosynthesis. It consists of the orotate base linked to a ribose sugar with a single phosphate group at the 5' position.

OMP is formed when orotate condenses with phosphoribosyl pyrophosphate (PRPP) in a reaction catalyzed by orotate phosphoribosyltransferase. The product, OMP, is then decarboxylated by orotidine-5'-phosphate decarboxylase to yield uridine monophosphate (UMP).

In many organisms, de novo pyrimidine synthesis uses a bifunctional enzyme, uridine monophosphate synthase (UMPS), that carries out both steps. In other species, the two activities reside on separate enzymes.

Defects in this pathway can cause metabolic disorders; in humans, defects in UMPS or related steps can lead to orotic aciduria, marked by elevated orotate excretion and megaloblastic anemia due to impaired UMP production.

OMP's role is primarily as an intermediate of nucleotide metabolism. It serves as a standard substrate in biochemical studies of pyrimidine biosynthesis and helps illuminate enzyme mechanisms within this pathway.