• Serine is a non-essential & glycogenic amino
acid.
• Glycine & serine are interconvertible.
• Serine is also synthesized from the
intermediates of glycolysis.
• Serine participates in transamination
reactions.
• It undergoes deamination to form pyruvate.
Serine dehydratase
Serine
PLP, NH3+
Pyruvate
• Serine is involved in one-carbon metabolism
• It donates methylene (-CH2) moiety to
tetrahydrofolate (THF).
Serine hydroxymethyl transferase
(PLP)
Serine
Glycine
THF
CH2-THF
• On decarboxylation (PLP dependent) serine
forms ethanolamine
• Ethanolamine is precursor for choline synthesis.
Serine
Ethanolamine
CO2
• 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.
• 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.
One carbon metabolism
Proteins
Glucose
Glycine
Alanine
Cysteine
Cystine
Sphingomyelins
Serine
Phosphatidyl serine
Selenocysteine
Ethanolamine
Choline
• 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.
• 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.
Glycine + acetaldehyde
Proteins
α- ketobutyrate
Propionyl CoA
Threonine
Aminoacetone
Pyruvate
Methylglyoxyl
Lactate
• Textbook of Biochemistry-U Satyanarayana
• Textbook of Biochemistry-DM Vasudevan
• Textbook of Biochemistry-MN Chatterjea