Regulation of cellular polyamines by antizyme

Proteins that are degraded by the proteasome are first modified by a set of enzymes that attach multiple copies of ubiquitin to substrate lysines, but a tiny minority, including the polyamine-synthesizing enzyme ornithine dec arboxylase, is handled differently. This enzyme is targeted for destruction by another protein - antizyme. Why does ornithine decarboxylase have its o wn dedicated destruction mechanism, how does it work, and is it the only pr otein to be targeted to the proteasome in this way?.