Spermine oxidase (SMO) is a recently described flavoenzyme belonging to the class of polyamine oxidases (PAOs) and participating in the polyamine metabolism in animal cells. In this paper we describe the expression, purification, and characterization of the catalytic properties of a recombinant mouse SMO (mSMO). The purified enzyme has absorbance peaks at 457 nm (epsilon = 11 mM(-1) cm(-1)) and 378 nm, shows a molecular mass of similar to63 kDa, and has K-m and k(cat) values of 170 muM and 4.8 s(-1), using spermine as substrate; it is unable to oxidize other free or acetylated polyamines. The mechanism-based PAO inhibitor N,N-1-bis(2,3-butadienyl)-1,4-butanediamine (MDL72,527) acts as a competitive inhibitor of mSMO, with an apparent dissociation constant K-i = 63 muM. If incubated for longer times, MDL72,527 yields irreversible inhibition of the enzyme with a half-life of 15 min at 100 muM MDL72,527. The mMSO catalytic mechanism, investigated by stopped flow, is consistent with a simple four-step kinetic scheme. (C) 2004 Elsevier Inc. All rights reserved.