Polyamine oxidases (PAOs), like MAOs, are also FAD-dependant and form aldehydes and hydrogen peroxide. PAOs are approximately 60KDa in size, are monomers and are located in peroxisomes. They act on endogenous polyamines as well as some xenobiotics. The polyamines of the spermine and spermidine families are important physiologically as they mediate cell function and growth and also play a role in programmed cell death. The balance between biosynthesis, degradation and uptake of these polyamines is strictly controlled in cells and the PAO system is one of a set of enzymes that maintains this regulation (Tabor & Tabor 1984, Benedetti 2001).