Lec14 amino synt

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Lec14 amino synt

  1. 1. Berg • Tymoczko • Stryer Biochemistry Sixth Edition Chapter 24:The Biosynthesis of Amino Acids Copyright © 2007 by W. H. Freeman and Company
  2. 2. BIOSYNTHESIS OF AMINO ACIDS All amino acids are synthesized from intermediates of Glycolysis, TCA or PPP. Different organisms vary greatly in their ability to synthesize the 20 amino acids. Amino acids are grouped by their metabolic precursors.
  3. 3. Several enzyme cofactors play importantroles in amino acid metabolism  One carbon transfer is very important – Biotin – Tetrahydrofolate – S-adenosylmethionine (SAM)
  4. 4. Tetrahydrofolate carriesactivated 1-C units atseveral oxidation levels
  5. 5. SAM is more commonly used for CH3 transfer.
  6. 6. Cys is made from Ser and HomoCys Sulfur comes from homoCys The C skeleton comes from Ser High homocysteine levels are associated with vascular diseases • Coronary heart disease • Arteriosclerosis The molecular basis of the disease ??? • It appears to damage cells lining blood vessels and to increase the growth of vascular smooth muscle cells
  7. 7. Amino acids are precursors of many biomolecules Glutathione (GSH) Nitric oxide (NO)
  8. 8. GSH serves as a buffer and antioxidant Protects cells from oxidative damage Presents at high levels (5 mM) It cycles between a reduced form (GSH) and an oxidized form (GSSG) GSSG is reduced to GSH by GSH reductase The ratio of GSH to GSSG is greater than 500 in most cells. GSH plays a key role in detoxification by reacting with hydrogen peroxide and organic peroxides. Glutathione peroxidase is remarkable in having a modified amino acid containing Se.
  9. 9. 2 GSH + RO OH GSSG + H2O + ROH
  10. 10. Nitric oxide is formed from Arg NO is an important messenger It is made by NO synthase NADPH and Oxygen are required
  11. 11. Amino acids are converted to specialized products Porphyrins and bile pigments – Biosynthesis of porphyrins • Formation of ALA • Formation of porphobilinogen Porphyrias – Congenital erythropoietic porphyria
  12. 12. Other specialized products Creatine Histamine Serotonin Catecholamines – Dopamine – Norepinephrine – Epinephrine Melanin Thyroid Hormones

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