Carbamoyl-phosphate synthetase II in kinetoplastids.

Genes for carbamoyl-phosphate synthetase II (CPS II), the first enzyme of de novo pyrimidine biosynthesis, were cloned from kinetoplastids, Trypanosoma cruzi and Leishmania mexicana. T. cruzi CPS II gene encodes a protein of 1524 amino acids that encompasses the glutaminase and CPS domains, but incorporates neither aspartate carbamoyltransferase nor dihydroorotase. The residue corresponding to lysine 993 of Escherichia coli CPS, a residue that characterizes the CPS inhibited by UMP and that is replaced by tryptophan in those inhibited by UTP, is in kinetoplastids a hydrophilic glutamine, in line with the preferential inhibition by UDP of kinetoplastid CPS II.