Characterization of maize polyamine oxidase.

Some structural and biochemical characteristics of polyamine oxidase (PAO) purified from maize shoots have been examined. The enzyme has only alanine as N-terminal amino acid and its N-terminal sequence shows a significant degree of homology with tryptophan 2-monooxygenase from Pseudomonas syringae pv. savastanoi. The pH optimum for the stability of the native enzyme is 5, similar to that of the barley leaf enzyme. Calorimetric analysis shows a single two-state transition at pH 6 with Tm 49.8 degrees. At pH 5 the thermal stability is increased by more than 14 degrees. Amine oxidation products, delta 1-pyrroline and diazabicyclononane, are competitive inhibitors of PAO activity (apparent Ki = 400 and 100 microM respectively). Moreover these compounds improve the thermal stability of the enzyme. N1-Acetylspermine, which is a good substrate for mammalian PAO, acts as a non-competitive inhibitor for the plant enzyme.