These two-steps are rapid and irreversible in mammals. In other pyrimidine auxotrophs that do not have this bifunctional enzyme, usually less complex organisms, two separate enzymes are required to carry out this reaction. Both orotidylate and uridylate are major pyrimidine nucleotides, as uridylate is a precursor to RNA.
In mammals, these two processes occur rapidly and irreversibly. In contrast, other pyrimidine auxotrophs that lack the bifunctional enzyme typically require two separate enzymes to accomplish this reaction. Both orotidylate and uridylate play crucial roles as major pyrimidine nucleotides, with uridylate serving as a precursor to RNA.