Figure 1.

Polyamine catabolic pathway in mammals. SSAT catalyzes the acetyl-group transfer from acetyl-CoA to the aminopropyl end of spermidine or spermine, producing N¹-acetylspermidine or N¹-acetylspermine, respectively. These acetylated PAs are either excreted from the cell or used as substrates for PAOX, producing H₂O₂, 3-acetoamidopropanal, and either putrescine or spermidine, depending on the starting substrate. Alternatively, spermine can be directly oxidized back to spermidine by SMOX while generating H₂O₂ and 3-aminopropanal.