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Break down of carbon skeleton (R side chain)
Catabolism of carbon skeleton leading to formation of one or more of
the following products: pyruvate, fumarate, α-ketoglutarate, succinyl
CoA, oxaloacetate, acetyl CoA and acetoacetate.
1- Amino acids whose catabolism yields: pyruvate, fumarate, αketoglutarate, succinyl CoA or oxaloacetate are known to be
glucogenic amino acids. These products are substrates for
gluconeogenesis and lead to glucose production.
Oxaloacetate is a substrate for gluconeogenesis by converting into to
phosphoenolpyruvate (PEP) which is then pass the reversal glycolysis
pathway (gluconeogenesis) to give finally glucose.
pyruvate, fumarate, α-ketoglutarate, succinyl CoA are intermediates of
kreb’s that can be converted into oxaloacetate which is converted into
glucose by gluconeogenesis as before
2- Amino acids whose catabolism yields acetoacetate (ketone
body) or its precursor; acetyl CoA or acetoacetyl CoA are known
to be ketogenic e.g. Leucine and Lysine are pure ketogenic.
3- Some amino acids are catabolized into both substrates of
gluconeogenesis (i.e. give glucose) and acetoacetate so they are
called: mixed ketogenic and glucogenic e.g phenylalanine,
tyrosine, tryptophan and isoleucine.
Glucogenic amino acids
Glucogenic amino acids that gives oxaloacetate:
1- Aspartate gives oxaloacetate by transamination
2- Aspargine by asparginase enzyme gives aspartate which gives
oxaloaetate by transamination
Glucogenic amino acids that gives pyruvate
1- Alanine: gives pyruvate by transamination
2- Serine
3- Glycine: glycine is converted into serine which is then
converted into pyruvate
4- Cysteine gives pyruvate by transamination
5- Threonine
6- **Tryptophan: is mixed glucogenic (gives pyruvate) and
ketogenic (gives acetyl CoA)
Glucogenic amino acids that gives α-ketoglutarate
1- Glutamate: gives α-ketoglutarate by two reactions:
A- transamination
B- oxidative deamination by GDH enzyme
Amino acids that gives α-ketoglutarate (continued)
2- Glutamine :by glutaminase is converted into glutamate
which gives α-ketoglutarate
3- Proline: which is oxidized into glutamic which gives αketoglutarate
4- histidine: is converted into glutamate which gives αketoglutarate
5- Arginine: gives ornithine which is then converted into
Glucogenic amino acids that gives fumarate:
**Phenyl alanine
** Tyrosine
Phenylalanine and tyrosine are mixed glucogenic (gives pyruvate)
and ketogenic(gives acetoacetate)
Glucogenic amino acids that gives succinyl CoA:
2- Threonine
3- Valine
4- Isoleucine**
Isoleucine is mixed glucogenic (gives succinyl CoA) and ketogenic
(gives acetyl CoA)