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 the context of pyrimidine metabolism, these two steps occur rapidly and irreversibly in mammals. In contrast, other organisms that lack the bifunctional enzyme typically require two separate enzymes to accomplish this reaction. Both orotidylate and uridylate play significant roles as major pyrimidine nucleotides, with uridylate serving as a precursor to RNA.