Spermine synthase (, spermidine aminopropyltransferase, spermine synthetase) is an enzyme that converts spermidine into spermine. This enzyme catalyses the following chemical reaction
S-adenosylmethioninamine + spermidine 5′-methylthioadenosine + spermine Spermine synthase is an enzyme involved in polyamine biosynthesis. In humans, it is coded by SMS (gene), but it is present in all eukaryotes and plays a role in a variety of biological functions in plants. Its structure consists of two identical monomers of 41 kDa with three domains each, creating a homodimer formed via dimerization. The interactions between one of the three domains, the N-terminals of the monomers, is responsible for dimerization as that is where the active site is located; the central terminal consisting of four β- strands structurally forming a lid for the third domain, the C-terminal domain.
Function The enzyme catalyses a reaction which transfers a three-carbon aminopropyl unit to spermidine. The source is S-adenosylmethioninamine:
The reaction is similar to one which produces spermidine from putrescine by action of spermidine synthase.
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