Dr.Prompt replacement of dietary protein by an amino acid mixture that lacks leucine, 
isoleucine, and valine averts brain damage and early mortality.Amar Babikir Elhussein
BSc, MSc & PhD
Biosynthesis of Nonessential Amino acids 
and Fate of Amino Acid Carbon Skeleton
Introduction:
?The major product of degradation of the carbon skeleton of the amino acids 
are pyruvate, intermediate of TCA cycle acetyl CoA and 
acetoacetate.Methionine: provide methyl group for synthesis of various compounds, it 
sulfur is incorporated into cysteine; and the remaining carbon form 
Succinyl CoA.The amino acids that are synthesized from intermediate of glycolysis are 
degraded to pyruvate ( Serine, Glycine, Cysteine and alanine).Four amino acids converted to Propionyl CoA, Which carboxylated in 
reaction require Biotin to form Methylmalonyl CoA, Which is rearranged 
to form Succinyl CoA in reaction require vitamin B12.Plasma and urinary levels of leucine, isoleucine, valine, ?-keto acids, and ?-hydroxy acids 
(reduced ?-keto acids) are elevated.The enzymes glutamate dehydrogenase, glutamine 
synthetase, and aminotransferases occupy central 
positions in amino acid biosynthesis.When the amino acid is degraded, the major products are Pyruvate, 
Intermediate of  TCA cycle, acetyl CoA or Acetoacetate.Tyrosine: Obtained from the diet or by hydroxylation of phenylalanine, 
is converted to Homogentisate, whose aromatic ring is opened and 
cleaved, forming fumarte.3) Glycine and cysteine:
Can be derived from Serine
Serine biosynthesis
II. Amino acid derived from TCA cycle:
1.?Arginine can produced in urea cycle via Ornithine 
which is produced by transamination of Glutamate 
semialdehyde.As the name implies, the odor of urine in maple syrup urine disease (branched-chain 
ketonuria) suggests maple syrup or burnt sugar.Ten of the nonessential amino acids contain carbon skeleton that may be 
derived from glucose.Four amino acids (Lysine, Threonine, Isoleucine and tryptophan), Can 
form acetyl CoA 
?Of the 20 amino acids commonly found in proteins, 11 are not essential in 
the adult diets because it can be synthesized in the body.Intermediate of glycolysis serve as precursor 
for Serine, glycine, cysteine and alanine.B. Proline and Arginine are derived from Glutamate 
semialdehyde which is formed by reduction of 
Glutamate.The eleven nonessential amino 
acid is synthesized by 
hydroxylation of the essential 
amino acid Phenyl alanine.Activity II catalyzes reduction of dihydrobiopterin by
NADPH, and activity I the reduction of O2 to H2O and 
of phenylalanine to tyrosine.Glycine: in a reversal of the reaction utilized for it synthesis, react with 
Methylene tetrahydrofolate to form serine.ii. Amino acids that are converted to intermediate of  TCA cycle:
?Carbons from 4 groups of amino acids from TCA cycle intermediates, ?Valine and Isoleucine: two of three branched chain amino acids, Form 
Succinyl CoA.i. Valine  is eventually converted to Succinyl CoA  via Propionyl CoA and 
Methylmalonyl CoA.ii. Isoleucine is converted to Succinyl CoA after two of it carbon are 
released as acetyl CoA.Tyrosine:
?- Ketoglutarate.?????2.3.4.???1.2.3.4.2.4.5.6.1.2.??3.2.3.2.??????