In this report we show that recombinant Saccharomyces cerevisiae Fms1 protein is a polyamine oxidase that binds FAD with an FAD:Fms1 stoichiometry of 1:1. Biochemical characterization of Fms1 shows that it can oxidize spermine, N-1-acetylspermine, N-1-acetylspermidine, and N-8-acetylspermidine, but not spermidine. The products of spermine oxidation are spermidine and 3-aminopropanal. A kinetic analysis revealed that spermine, N-1-acetylspermine, and N-1-acetylspermidine are oxidized with similar efficiencies, while N-8-acetylspermidine is a poor substrate. The data support a previous report, suggesting that Fms1 is responsible for the production of beta-alanine from spermine for the synthesis of pantothenic acid. (C) 2003 Elsevier Science (USA). All rights reserved.