The discovery of an inducible oxidase whose apparent substrate preference is spermine indicates that polyamine catabolism is more complex than that originally proposed. To facilitate the study of this enzyme, the purification and characterization of the recombinant human PAOh1/SMO polyamine oxidase are reported. Purified PAOh1/SMO oxidizes both spermine (K(m)=1.6 microM) and N(1)-acetylspermine (K(m)=51 microM), but does not oxidize spermidine. The purified human enzyme also does not oxidize eight representative antitumor polyamine analogues; however, specific oligamine analogues were found to be potent inhibitors of the oxidation of spermine by PAOh1/SMO. The results of these studies are consistent with the hypothesis that PAOh1/SMO represents a new addition to the polyamine metabolic pathway that may represent a new target for antineoplastic drug development.