Purification of homogeneous glutamine-dependent carbamyl phosphate synthetase from ascites hepatoma cells as a complex with aspartate transcarbamylase and dihydroorotase

Abstract

Glutamine-dependent carbamyl phosphate synthetase [EC 2.7.2.9] was purified 1,300-fold from rat ascites hepatoma cells (AH 13) as a multienzyme complex with aspartate transcarbamylase[EC 2.1.3.2] and dihydroorotase[EC 3.5.2.3], using dimethyl sulfoxide, glycerol, and dithiothreitol as stabilizers. The purified complex was essentially homogeneous on agarose-acrylamide composite gel electrophoresis and analytical ultracentrifugation. Its molecular weight was estimated to be about 870,000 by sedimentation equilibrium studies. After alkylation with iodoacetamide or reduction with 0.6% dithiothreitol at 100 degrees, the complex gave a single band on polyacrylamide gel electrophoresis in sodium dodecyl sulfate in a position corresponding to a molecular weight of 210,000. These results indicate that the complex consists of four subunits of similar size.