Orotic acid

Orotic acid is a heterocyclic compound and an acid; it is also known as pyrimidinecarboxylic acid. It was once believed to be part of the vitamin B complex and was called vitamin B13, but it is now known that it is not a vitamin but is instead manufactured in the body by intestinal flora.

Its salts, known as orotates, are sometimes used as mineral carriers in some dietary supplements, to increase their bioavailability. Lithium orotate is the most frequently used in this manner.

Synthesis of orotate
Dihydroorotate is synthesized to orotic acid by the enzyme dihydroorate dehydrogenase, where it later combines with phosphoribosyl pyrophosphate (PRPP) to form orotidylate (OMP). A distinguishing characteristic of pyrimidine synthesis is that the pyrimidine ring is fully synthesized before being attached to the ribose sugar, whereas purine synthesis happens by building the base directly on the sugar.

Orotic acid diseases
A buildup of orotic acid can lead to orotic aciduria. It may be a symptom of an increased ammonia load due to a metabolic disorder, such as a urea cycle disorder.

In ornithine transcarbamoylase deficiency, a disorder of the urea cycle, excess carbamoyl phosphate is converted into orotic acid. This typically leads to increased urinary orotic acid excretion, because the orotic acid is not being properly utilized and must be eliminated.

Orotic acid can be mutagenic (causes mutations) in mammalian somatic cells. It is also mutagenic for bacteria and or yeast.