This document summarizes amino acid biosynthesis and metabolism. It discusses how amino acids are synthesized from intermediates of glycolysis, the TCA cycle, or the pentose phosphate pathway. It also describes how certain cofactors like biotin, tetrahydrofolate, and S-adenosylmethionine play important roles in amino acid metabolism, especially in one-carbon transfer reactions. Additionally, it explains how amino acids are precursors to important biomolecules like glutathione, nitric oxide, porphyrins, bile pigments, creatine, histamine, and specialized hormone products.

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

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.

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

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

20. SAM is more commonly used for CH3 transfer.

26. 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

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

30. 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.

33. 2 GSH + RO OH GSSG + H2O + ROH

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

38. Amino acids are converted to
specialized products
 Porphyrins and bile pigments
– Biosynthesis of porphyrins
• Formation of ALA
• Formation of porphobilinogen
 Porphyrias
– Congenital erythropoietic porphyria

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