Download AMINO ACID DEGRADATION

SEVEN AMINO ACIDS DEGRADED TO
ACETYL COA
THE EXCRETION OF AMMONIUM IONS
• A part of NH4+ that is formed in the degradation of
amino acids is used for the biosynthesis of nitrogen
compounds. In most of the land living vertebrates
the excess NH4+ is converted in urea and in that
form is excreted. In birds and reptiles it is converted
into uric acid and in aquatic animals it is directly
excreted as urea.
DESTINATION OF DEGRADED
AMINO ACID IN THE METABOLISM
• The carbon atoms of degraded amino acids are found in
important intermediate products of the metabolism that can
be converted into glucose or can be oxidized in the CITRIC
ACID CYCLE. The carbon skeletons of the twenty amino acids
are brought back to only seven molecules : pyruvate, acetyl
CoA, acetoacetyl CoA, alpha-ketoglutarate, succinyl CoA,
fumerate and oxaloacetate. Amino acids that are degraded to
acetyl CoA are called KETOGENIC AMINO ACIDS because they
can be converted into ketone bodies. The amino acids that
are converted in the remaining of the seven molecules are
called GLUCOGENIC AMINO ACIDS becaause they can be
converted into phosphoenol pyruvate and then in glucose.
• Some amino acids are both ketogenic as well as glucogenic for
example tyrosine, phenylalanine etc.
Some amino
acids are both
ketogenic as well
as glucogenic for
example tyrosine,
phenylalanine
etc.
The C3 family: alanine, serine and cystein is converted in pyruvate. Pyruvate is the entry point
for alanine, serine, cysteine, glycine, threonine and can be converted into pyruvate through
different paths, by which the sulphur atom returns in hydrogen sulphide and sulphate. Also
carbon atoms of amino acids glycine, threonine and tryptophan can be converted into pyruvate.
The C4 family aspartate and asparagine are converted in oxaloacetate. Aspartate can also be
converted in fumeratye by urea cycle. Fumerate is an entry point for half of the carbon atams of
tyrosine ans phenylalanine.
• The C5 family glutamine, proline, arginine and hystidine are converted to alphaketaglutarate via glutamate. Alpha-ketoglutarate is the entry point for glutsamine,
proline, arginine and hystidine that are first converted to glutam,ate.
• Succinate CoA is an entry point for single apolar amino acids by the transformation
of threonine, isoleucine and valine via propionyl CoA. The pathway of propionyl
CoA to succinate CoA is also present in thre oxidation of fatty acids with an odd
number carbon atoms which are thus partial glucogenic, three of their carbon
atoms can go in glucose.
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