Human Liver Argininosuccinase Purification and Partial

Argininosuccinase from normal human liver was purified and characterized. The properties of this enzyme were compared to those of argininosuccinase from bovine liver. The molecular weight of the native human liver enzyme is 200,000 as determined by gel filtration. Polyacrylamide disc gel electrophoresis of the enzyme, dissociated by sodium dodecyl sulfate, indicated that it exists as a tetramer of identical or similar subunits of 50,000 daltons. No evidence of multiple species was found during the purification or subsequent characterization. The enzyme was inactivated in cold and reactivated by thermal incubation. These properties were similar to those observed for bovine liver enzyme. However, unlike bovine liver argininosuccinase, human liver enzyme exhibited normal Michaelis-Menten kinetics both in phosphate and Tris buffers, and the apparent Michaelis constant for L-argininosuccinate was 0.1 mM. It failed to show any negative homotropic interactions with substrate, and nucleotide GTP had no effect on K,,, or Vmm.