Polyamines play a major role in very basic genetic processes such as DNA synthesis and gene expression. Spermine and spermidine bind to the phosphate backbone of nucleic acids. This interaction is mostly based on electrostatic interactions between positively charged ammonium groups of the polyamines and the negatively charged phosphates of the nucleic acids.
Polyamines are key to cell migration, proliferation and differentiation in plants and animals. The metabolic levels of polyamines and amino acid precursors are critical and hence biosynthesis and degradation are tightly regulated.
Polyamines represent a group of plant growth hormones, but they also have an effect on skin, hair growth, female fertility, fat depots, pancreatic integrity and regenerative growth in mammals. In addition, spermine is an important reagent widely used to precipitate DNA in molecular biology protocols. Spermidine stimulates activity of T4 polynucleotide kinase and T7 RNA polymerase and is therefore used in protocols employing these enzymes.
Spermine and spermidine are derivatives of putrescine (1,4-diaminobutane) which is produced from L-ornithine by action of ODC (ornithine decarboxylase). L-ornithine is the product of L-arginine degradation by arginase.
Spermidine is a triamine structure that is produced by spermidine synthase (SpdS) which catalyzes monoalkylation of putrescine (1,4-diaminobutane) with decarboxylated S-adenosylmethionine (dcAdoMet) 3-aminopropyl donor. The formal alkylation of both amino groups of putrescine with the 3-aminopropyl donor yields the symmetrical tetraamine spermine.
The biosynthesis of spermine proceeds to spermidine by the effect of spermine synthase (SpmS) in the presence of dcAdoMet. The 3-aminopropyl donor (dcAdoMet) is derived from S-adenosylmethionine by sequential transformation of L-methionine by methionine adenosyltransferase followed by decarboxylation by AdoMetDC (S-adenosylmethionine decarboxylase).
Hence, putrescine, spermidine and spermine are metabolites derived from the amino acids L-arginine (L-ornithine, putrescine) and L-methionine (dcAdoMet, aminopropyl donor).
Polyamine levels are tightly regulated, and are therefore kept within a narrow range. This regulation occurs to a significant extent by the activity of ODC and AdoMetDC, which are the enzymes responsible for the production of the polyamine building blocks putrescine and dcAdoMet. Spermine and spermidine levels are also affected by the rate of conversion of their respective precursors, putrescine and spermine. Furthermore, it is known that the reverse conversions of spermine to spermidine and spermidine to putrescine are important as well. These reactions proceed in a different manner and involve the action of spermine oxidase (SMO) or acetylpolyamine oxidase (PAO) on the acetylated polyamines. Acetylation of spermine and spermidine is catalyzed by SSAT (spermidine/spermine-N1-acetyltransferase).
The key enzyme in the regulation of polyamine levels appear to be ODC, AdoMetDC and SSAT.
Most of these insights arose from research involving genetic engineering of polyamine metabolism in transgenic rodents. These studies were undertaken in an effort to unravel complex cellular functions.
It was established that expression of key enzymes effects spermatogenesis, skin physiology, promotion of tumor growth, female fertility and regenerative growth.
Moreover, research revealed that rodents with deleted ODC or AdoMetDC genes die at an early stage of development. Deletion of SmpS gene in male mice causes sterility, severe neuronal abnormalities and early death. Recently, it was suggested that ODC antizyme (inhibits and degrades ODC) may act as a tumor suppressor. The effects of polyamines on hair growth is also illustrated by eflornithine, an irreversible inhibitor of ODC that has been approved for treatment of unwanted facial hair growth.
Juhani Jänne, Leena Alhonen, Marko Pietilä and Tuomo A. Keinänen, Genetic approaches to the cellular functions of polyamines in mammals, Eur. J. Biochem. 2004, 271, 877-894
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