ABSTRACT
The eld of polyamine research has blossomed in recent years as a result of the many physiological aspects of cellular metabolism and differentiation in which they are involved. As repeatedly mentioned in previous chapters, polyamine chemical structure is simple; they are aliphatic organic compounds containing amino groups. Ornithine decarboxylase (Odc) or/and arginine decarboxylase (Adc) in plants, spermidine synthase (Spds), S-adenosylmethionine (SAM) decarboxylase (Samdc), and spermine synthase (Spms) are the enzymes implied in the biosynthesis of polyamines. The simplest one is putrescine, a compound that originated from the decarboxylation of l-ornithine or arginine in the case of plants by Odc or Adc, respectively. An aminopropyl group is added to putrescine by Spds to form spermidine. Decarboxylated SAM (dcSAM) is the donor of aminopropyl groups, and it is generated from SAM by the action of Samdc. The addition of another aminopropyl group to spermine then leads to the synthesis of spermine, a reaction catalyzed by Spm (Tabor and Tabor 1984). Polyamine back-conversion consists of the transformation of spermine back to spermidine and of spermidine back to putrescine. First, spermidine/spermineN1-acetyl transferase (Ssat) transfers an acetyl group from acetyl coenzyme A to the N1 position of spermine or spermidine. Subsequently, polyamine oxidase (Pao) catalyzes the oxidative deamination of acetylated polyamines into spermidine and putrescine, respectively (Pegg and McCann 1982; Casero and Pegg 1993). For a more detailed description of all these processes, see Chapter 3.
