Aspartate transcarbamoyl transferase (ATCase)

Aspartate transcarbamoyl transferase (ATCase) is a key enzyme in the de novo biosynthesis of pyrimidine nucleotides. It catalyzes the committed step in this pathway: the condensation of carbamoyl phosphate and L-aspartate to form N-carbamoyl-L-aspartate and inorganic phosphate. This reaction is essential for producing pyrimidine rings, which are building blocks for DNA and RNA. ATCase activity is tightly controlled by feedback inhibition (CTP) and activation (ATP), ensuring balanced production of purines and pyrimidines within cells. The holoenzyme consists of six catalytic and six regulatory subunits, displaying classic allostery with two main conformational states (T and R). While most detailed studies focus on *E. coli*, similar structures have been solved from other organisms.

Inhibition of pyrimidine biosynthesis