SERINE & THREONINE METABOLISM

2. • Serine is a non-essential & glycogenic amino
acid.
• Glycine & serine are interconvertible.
• Serine is also synthesized from the
intermediates of glycolysis.

3. • Serine participates in transamination
reactions.
• It undergoes deamination to form pyruvate.
Serine
PLP, NH3
+
Pyruvate
Serine dehydratase

4. • Serine is involved in one-carbon metabolism
• It donates methylene (-CH2) moiety to
tetrahydrofolate (THF).
Serine
THF
Glycine
Serine hydroxymethyl transferase
(PLP)
CH2-THF

5. • On decarboxylation (PLP dependent) serine
forms ethanolamine
• Ethanolamine is precursor for choline synthesis.
Serine
CO2
Ethanolamine

6. • Serine is utilized for the synthesis of cysteine.
• Entire cysteine molecule is derived from
serine except the sulfur that comes from
homocysteine.
• Serine is involved in the formation of
selenocysteine, the 21st amino acid found in
certain proteins.

7. • Serine is directly participates in the synthesis
of phospholipid-phosphatidyl serine.
• Serine is involved in the synthesis of
sphingomyelins & cephalins.
• Serine OH group serves as a carrier of
phosphate which involved in the regulation
of many enzyme activities.

8. Serine
Proteins
Glucose
Glycine
Alanine
Cysteine
Cystine
One carbon metabolism
Sphingomyelins
Phosphatidyl serine
Selenocysteine
Ethanolamine
Choline

9. • Threonine is essential amino acid.
• It is glycogenic & does not participate in
transamination reactions.
• Threonine is also a carrier of phosphate group
in the protein structure.
• Threonine undergoes deamination by
threonine dehydratase to α-ketobutyrate
which is converted to propionyl CoA.

10. • Threonine can be cleaved to glycine &
acetaldehyde by serine hydroxymethyl
transferase.
• Dehydrogenation followed by
decarboxylation of threonine results in
aminoacetone which may be converted to
pyruvate or lactate.

11. Threonine
Proteins
α- ketobutyrate
Propionyl CoA
Glycine + acetaldehyde
Aminoacetone
Pyruvate
Lactate
Methylglyoxyl

12. • Textbook of Biochemistry-U Satyanarayana
• Textbook of Biochemistry-DM Vasudevan
• Textbook of Biochemistry-MN Chatterjea