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BiochemistrySixth Edition
Chapter 24:The Biosynthesis of Amino
Acids
Copyright © 2007 by W. H. Freeman and Company
Berg • Tymoczko • Stryer
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.
Several enzyme cofactors play important roles in amino acid metabolism
One carbon transfer is very important– Biotin– Tetrahydrofolate– S-adenosylmethionine (SAM)
Tetrahydrofolate carries activated 1-C units at several oxidation levels
SAM is more commonly used for CH3 transfer.
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
Amino acids are precursors of many biomolecules
Glutathione (GSH) Nitric oxide (NO)
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.
2 GSH + RO OH GSSG + H2O + ROH
Nitric oxide is formed from Arg
NO is an important messenger It is made by NO synthase NADPH and Oxygen are required
Amino acids are converted to specialized products
Porphyrins and bile pigments– Biosynthesis of porphyrins
• Formation of ALA• Formation of porphobilinogen
Porphyrias– Congenital erythropoietic porphyria
Other specialized products
Creatine Histamine Serotonin Catecholamines
– Dopamine– Norepinephrine– Epinephrine
Melanin Thyroid Hormones