Fate of Amino Acid Nitrogen: Transamination Reactions
Transamination: – a major process for transferring
and removing nitrogen from amino acids - catalyzed
by transaminases 0r aminotransferases - the
nitrogen is transferred as an amino group from the
original amino acid to α-ketoglutarate, forming
glutamate – the amino acid is converted to α-keto
acid
– e.g. aspartate is transaminated to the α-keto acid,
Oxalo acetate and α-ketoglutarate to glutamate
•all AAs except Lys and Thr can
undergo transamination
•for most of these reactions,
α-ketoglutarate-glutamate serve as
one of the α-keto AA pairs
•pyridoxal phosphate (PLP - from
vitamin B6 - pyridoxine) is the
cofactor - the amino group of
one AA becomes the amino group
of a 2nd AA
•these reactions are fully
reversible
– can add nitrogen to α-keto acids
to form AAs
– therefore have a role in both AA
degradation and synthesis
Pyridoxal Phosphate (PLP)
•derived from pyridoxine
(Vitamin B6)
•cofactor for transamination
(aminotransferase) reactions
•cofactor for decarboxylations
and a number of other
reactions involving amino
acids
Functions of Pyridoxal Phosphate in Transamination
•enzyme bound PLP reacts with AA1 forming Schiff’s
base (α-amino + PLP aldehyde)
•shift in double bond
•α-keto acid is released producing pyridoxamine
phosphate
•formation of Schiff’s base with α-keto acid2
•shift in the double bond
AA2 is released, enzyme bound pyridoxal
phosphate is regenerated
amino group of AA1 has been transferred to AA2