The Effect of Purine and Pyrimidine Nucleotides on Aspartate Transcarbamylase in Dictyostelium discoideum

Abstract

A key point in the regulation of pyrimidine biosynthesis by prokaryotic organisms is the enzyme Aspartate Transcarbamylase. This enzyme catalyzes the reaction of carbamyl phosphate plus aspartate to yield carbamyl aspartate, the first unique step in pyrmidine biosynthesis. While in prokaryotes ATCase appears as the main regulation factor, information on a control system for eukaryotic organisms is not well established. Studies done on Dictyostelium discoideum, a simple differentiating eukaryotic organism, have been carried out to discover what type of regulation it possesses over pyrimidine biosynthesis. ATCase enzyme assays performed using cytidine 5’-triphosphate and adenosine 5'-triphosphate resulted in no activation or inhibition of the enzymes' activity by these effectors. It appears that asparate transcarbamylase in D. discoideum is not allostericly regulated by pyrimidine or purine nucleotides.