1.
BiochemistrySixth Edition
Chapter 24:
The Biosynthesis of Amino Acids
Copyright © 2007 by W. H. Freeman and Company
Berg • Tymoczko • Stryer

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.
Several enzyme cofactors play important
roles in amino acid metabolism
 One carbon transfer is very important
– Biotin
– Tetrahydrofolate
– S-adenosylmethionine (SAM)

4.
Tetrahydrofolate carries
activated 1-C units at several
oxidation levels

5.
SAM is more commonly used for CH3 transfer.

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.
Amino acids are precursors of
many biomolecules
 Glutathione (GSH)
 Nitric oxide (NO)

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.
2 GSH + RO OH GSSG + H2O + ROH

10.
Nitric oxide is formed from Arg
 NO is an important messenger
 It is made by NO synthase
 NADPH and Oxygen are required

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.
Other specialized products
 Creatine
 Histamine
 Serotonin
 Catecholamines
– Dopamine
– Norepinephrine
– Epinephrine
 Melanin
 Thyroid Hormones