POLYAMINES
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This document discusses polyamine synthesis and metabolism. It notes that ornithine and S-adenosylmethionine are precursors for polyamine synthesis. Ornithine decarboxylase converts ornithine to putrescine, and putrescine is then converted to spermidine and spermine with involvement of S-adenosylmethionine and decarboxylated S-adenosylmethionine. Polyamine oxidase can break down polyamines by oxidizing spermine to spermidine and putrescine, which are then excreted. Polyamines are involved in nucleic acid and protein synthesis.
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POLYAMINES
- 2. The decarboxylation of amino acids or their derivatives results in formation of amines. Amino acid Amine Decarboxylase, PLP CO2
- 3. Polyamines possess multiple amino groups. Putrescine, spermine & spermidine are biologically important polyamines. Spermine & spermidine were detected in human semen.
- 4. Ornithine & S-adenosylmethionine are the precursors for polyamine synthesis. The four carbon moiety of SAM (not the methyl group) involved in polyamine formation. Ornithine decarboxylase acts on ornithine to split off CO2 & produce putrescine.
- 5. Ornithine decarboxylase has short half life (10 minutes). It is a regulatory enzyme in polyamine synthesis. Its activity is increased by corticosteroids, testosterone & GH. Putrescine is converted to spermidine & spermine with the involvement of SAM.
- 6. SAM is decarboxylated to give decarboxylated SAM. SAM decarboxylase is a rare example, does not require PLP as coenzyme. The propylamino group of decarboxylated SAM is transferred to putrescine to give spermidine.
- 7. Synthesis of spermine requires one more molecule of decarboxylated SAM & this reaction is catalyzed by spermine synthase.
- 10. The enzyme polyamine oxidase (liver peroxisomes) oxidizes spermine to spermidine & then to putrescine.
- 11. Spermidine & putrescine are excreted in urine in a conjugated form, as acetylated derivatives. Some amount of putrescine is also oxidized to NH3 & CO2.
- 12. Polyamines are basic in nature & possess multiple positive charges. They are associated with nucleic acids (DNA & RNA). They are involved in the synthesis of DNA, RNA & proteins.
- 13. Textbook of Biochemistry – U Satyanarayana Textbook of Biochemistry – DM Vasudevan