Figure 2.

Schematic representation of polyamine biosynthesis. The most important biosynthetic pathway begins with the action of arginase on arginine, forming ornithine, and its subsequent decarboxylation provides putrescine (PUT). PUT may also be obtained from arginine via decarboxylation to agmatine and subsequent action of agmatinase (left column). In addition, ornithine may be obtained from arginine and glycine via arginine-glycine-amidinotransferase. Glutamate and proline provide additional sources (middle columns). The additional carbon chains of spermidine and spermine are derived from methionine (right column).