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The polyamines are organic compounds having two or more primary amino groups - such as putrescine, cadaverine, spermidine, and spermine - that are growth factors in both eucaryotic and procaryotic cells.
Cyclen is the main representative of a class of cyclic polyamines. Polyethylene amine is a polymer based on aziridine monomer.
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Functions
Though it is known that polyamines are synthesized in cells via highly-regulated pathways, their actual function is not entirely clear. As cations, they bind to DNA, and, in structure, they represent compounds with cations that are found at regularly-spaced intervals (unlike, say, Mg++ or Ca++, which are point charges).
If cellular polyamine synthesis is inhibited, cell growth is stopped or severely retarded. The provision of exogenous polyamines restores the growth of these cells. Most eukaryotic cells have a polyamine transporter system on their cell membrane that facilitates the internalization of exogenous polyamines. This system is highly active in rapidly proliferating cells and is the target of some chemotherapeutics currently under development.1
Polyamines are also important modulators of a variety of ion channels, including NMDA receptors and AMPA receptors. They block inward-rectifier potassium channels so that the currents of the channels are inwardly rectified, thereby the cellular energy, i.e. K+ ion gradient across the cell membrane, is conserved.
Synthesis of linear polyamines
Putrescine
Putrescine is synthesized biologically via two different pathways, both starting from arginine.
- In one pathway, arginine is converted into agmatine, with a reaction catalyzed by the enzyme arginine decarboxylase (ADC); then agmatine is transformed into carbamilputrescine by agmatine imino hydroxylase (AIH). Finally, carbamilputrescine is converted into putrescine.
- In the second pathway, arginine is converted into ornithine and then ornithine is converted into putrescine by ornithine decarboxylase (ODC).
Cadaverine
Cadaverine is synthesized from lysine in a one-step reaction with lysine decarboxylase (LDC).
Spermidine and spermine
Spermidine is synthesized from putrescine, using an aminopropylic group from decarboxylated S-adenosyl-L-methionine (SAM). The reaction is catalyzed by spermidine synthase.
Spermine is synthesized from the reaction of spermidine with SAM in the presence of the enzyme spermine synthase .
References
- ^ Wang, C.; Delcros, J.-G.; Cannon, L.; Konate, F.; Carias, H.; Biggerstaff, J.; Gardner, R.; Phanstiel, O. Defining the molecular requirements for the selective delivery of polyamine-conjugates into cells containing active polyamine transporters. J. Med. Chem. 2003, 46, 5129-5138.
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- This page was last modified on 18 November 2008, at 07:20.
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