smokers has a higher concentration of orotic acid than that of a non smoking woman. It is reasoned that the smoking causes the pyrimidine biosynthesis process in the mother to be altered thus causing the orotic acid concentration to increase. . A modified orotic acid (5-fluoroorotic acid) is toxic to yeast. The mutant yeasts which are resistant to 5-fluoroorotic acid require a supply of uracil. See also Magnesium orotate Pyrimidine biosynthesis References Further reading External links Pyrimidinediones Enoic acids