BIOSYNTHESIS OF AMINO ACIDS

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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.

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Amino acid biosynthetic families grouped by
metabolic precursor
essential in the young Essential amino acids
PVT TIM HALL
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Amino acid Biosynthesis is regulated by feedback
inhibition.

• Sequential feedback inhibition
• Enzyme multiplicity
• Concerted feedback inhibition
• Cumulative feedback inhibition

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Several enzyme cofactors play important roles in
amino acid metabolism

• One carbon transfer is very important
• Biotin
• Tetrahydrofolate
• S-adenosylmethionine (SAM)

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Some enzyme cofactors in C-transfer reactions
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Tetrahydrofolate carries activated 1-C units at
several oxidation levels
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SAM is more commonly used for CH3 transfer...
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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 ???
• Perhapsdamage to cells lining blood vessels and
  increase the growth of vascular smooth muscle
  cells

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Amino acids are precursors of many biomolecules

• Glutathione (GSH)
• Nitric oxide (NO)

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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/GSSG------gt500
• 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.

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2GSH ROOH------gt GSSG H2O ROH
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Nitric oxide is formed from Arg

• NO is an important messenger
• It is made by NO synthase
• NADPH and Oxygen are required

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Amino acids are converted to specialized products

• Porphyrins and bile pigments
• Biosynthesis of porphyrins
• Formation of ALA
• Formation of porphobilinogen
• Porphyrias
• Congenital erythropoietic porphyria

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Other specialized products

• Creatine
• Histamine
• Serotonin
• Catecholamines
• Dopamine
• Norepinephrine
• Epinephrine
• Melanin
• Thyroid Hormones

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