carbamoyl phosphate + L-aspartate = H(+) + N-carbamoyl-L-aspartate + phosphate Pyrimidine metabolism; UMP biosynthesis via de novo pathway; (S)-dihydroorotate from bicarbonate: step 2/3. Heterododecamer (2C3:3R2) of six catalytic PyrB chains organized as two trimers (C3), and six regulatory PyrI chains organized as three dimers (R2). Belongs to the aspartate/ornithine carbamoyltransferase superfamily. ATCase family.