The reactions catalyzed by aminopropyl-transferases annotated above are generally irreversible. But spermine and spermidine can be recycled respectively into spermidine and putrescine. These events require the formation of N-acetylated intermediates, N1-acetylspermine and N1-acetylspermidine catalyzed by a cytosolic acetyl-CoA:spermidine/spermine N1-acetyl-tranferase (SSAT) enzyme.
Subsequently, polyamine-oxidase (PAO), a FAD enzyme present in the peroxysomes, yields a polyamine with release of an aldehyde (3-acetamindopropanal) and H2O2.
In addition, SMOX, a FAD-dependent, polyamine oxidase (PAOh1/SMO) that can efficiently use spermine as a substrate and is involved in interconversion reactions.