Kinetic properties of carbamoyl-phosphate synthetase II (glutamine-hydrolyzing) in the parasitic protozoan Crithidia fasciculata and separation of the enzyme from aspartate carbamoyltransferase.

A high specific activity of carbamoyl-phosphate synthetase II (glutamine-hydrolyzing; EC 6.3.5.5) was demonstrated in extract of the cultured Crithidia fasciculata. The enzyme was separated from aspartate carbamoyltransferase by ammonium sulfate fractionation. Apparent Km for the synthetase for L-glutamine, NH4+, MgATP or bicarbonate was 0.27, 26, 1.7 or 1.7 mM at 2.0% dimethyl sulfoxide plus 0.3% glycerol. 8.6% dimethyl sulfoxide plus 1.4% glycerol decreased Km for L-glutamine to 0.10 mM, while Km for MgATP was unaffected. The higher solvent concentrations made Vmax markedly reduced, yielding the inhibition of the activity. These properties are unique to the Crithidia synthetase, compared with the mammalian enzyme.