title: Influence of salts on the activity and the subunit structure of ornithine decarboxylase from rat liver.
abstract: The influence of salts on the subunit structure and the kinetics of purified rat ornithine decarboxylase (L-ornithine carboxy-lyase, EC 4.1.1.17) was examined. Salts were found to cause subunit dissociation of the enzyme, producing the monomeric form of molecular weight 55 000 in the presence of 0.25 M NaCl/10 mM sodium phosphate buffer (pH 7.0): the molecular weight was estimated to be 150 000 in 10 mM and 250 000 in 1 mM sodium phosphate buffer. Inclusion of NaCl in kinetic assays of rat ornithine decarboxylase had little effect on maximal velocity. However, the Km value for L-ornithine was dramatically increased with increasing sodium chloride concentration: the presence of 0.25 M NaCl resulted in a 10-fold increase of the Km. Thus, the presence of salts caused dramatic changes both in the subunit structure and in the catalytic property of the enzyme, although a direct correlation between both the changes was not evidenced.
mesh_terms: D000818:Animals; D007700:Kinetics; D008099:Liver / Q000201:enzymology*; D046911:Macromolecular Substances; D009955:Ornithine Decarboxylase; D065108:Ornithine Decarboxylase Inhibitors; D009994:Osmolar Concentration; D051381:Rats; D012492:Salts / Q000494:pharmacology
chemical_list: D046911:Macromolecular Substances; D065108:Ornithine Decarboxylase Inhibitors; D012492:Salts; D009955:Ornithine Decarboxylase