Assay of Spermidine and Spermine Synthases

Spermidine and spermine syntheses carry out the transfer of aminopropyl groups from decarboxylated S -adenosylmethionine (dcAdoMet) to putrescine and spermidine, respectively. Despite the close similarity of these reactions, they are totally distinct enzymes. Spermidine synthase (E. C. 2.5.1.16), which is present in virtually all organisms, transfers the aminopropyl group from dcAdoMet to putrescine forming spermidine. Spermine synthase (E. C. 2.5.1.22), which has a much more limited distribution and is absent from many prokaryotes, transfers the aminopropyl group to spermidine forming spermine. The cDNAs for both enzymes have been cloned and expressed and the derived amino acid sequences show little similarity except in the putative dcAdoMet binding site (1 –3 ).