Purification and properties of ornithine decarboxylase from Lactobacillus sp. 30a

Inducible ornithine decarboxylase from Lactobacillus sp. 30a has been purified to homogeneity as judged by ultracentrifugation and gel electrophoresis. Unlike histidine decarboxylase from the same species (a pyruvoyl enzyme), ornithine decarboxylase is a pyridoxal phosphate enzyme. The purified enzyme is specific for L-pornithine (Km 1.7 mM; specific activity, 150 to 200 mumol min-1 mg-1 at 37 degrees C) and is inhibited by various homologous omega-amino acids, amines, and polyamines. The native enzyme has an isoelectric point of 4.55 and a molecular weight of 1.04 X 10(6). At pH 7.3 and above, it dissociates reversibly to a species of Mr = 184,000, and on gel electrophoresis in the presence of sodium dodecyl sulfate shows a single band of Mr = 85,000. We ascribe these species to the dodecamer, dimer, and monomer, respectively, of a single peptide subunit; electron micrographs show a hexagonal array of apparently dimeric subunits in the native enzyme. Highest enzymatic activity is present in the dodecamer. The holoenzyme is resolved by dialysis against cysteine; spectrophotoemetric titration of the apoenzyme with pyridoxal 5'-phosphate indicates the presence of 1 coenzyme-binding site/monomeric subunit.