Essential amino acids
-
Non-essential amino acids
-
Root nodule of the pea plant protects
- The nitrogenase enzyme form degradation by oxygen
There is an obligate requirement for nitrogen to
- Synthesize mino acids
Nitrogen, nitrites, and nitrates are used by bacteria and plants, then
- We assimilate them into our diet
The liver is the major organ responsible for
- Nitrogen metabolism
- Amino acid biosynthesis
Amino acids synthesized in the liver
- Glutamate
- Glutamine
- Alanine
The most significant reactions in the pathways of amino acids are
- Glutamate dehydrogenase (reversible)
- Transamination reactions
- One-carbon transfers
Glutamate dehydrogenase
- Mitochondrial enzyme
- NH3 donated to alpha-ketoglutarate (forms AA glutamate at high livels of NH3)
One-carbon transfers are mediated by either
- Tetrahydrofolate
- S-adenosylmethionine
One 10 of the amino acids required are synthesized
- de novo (non-essential amino acids)
Non-essential amino acids are made
- By the body
Biosynthesis achieved by
- Simple reaction sequences
Essential amino acids must be provided
- In the diet
In infants (+ve N balance) with high urea cycle activity,
- Arginine becomes essential in the diet
Tyrosine is really misclassified since its made from
- The essential amino acid phenylalanine
Although mammals synthesize arginine,
- They cleave most of it to form urea
Phenylalanine hydroxase
- Allows us to convert tyrosine to phenylalanine
Amino acids can also be made with a wide range of
- Synthetic pathways
- 6 basic groups
Oxaloacetate (also in CAC and gluconeogenesis) can be used to make
- Aspartate
- Aspartate can then make arginine, methionine, threonine (then isoleucine), lysine
Pyruvate can be used to make
- Alanine
- Valine
- Leucine
Riobse-5-phopshate can by synthetically converted to
- Histidine
3-phosphoglycerate can be used to make
- Serine (AA)
- Serine can then make cysteine and glycine
Pyruvate (also in …) can be used to make
- Alanine
- Valine
- Leucine
Riobse-5-phopshate (also in …) can by synthetically converted to
- Histidine
3-phosphoglycerate (also in …) can be used to make
- Serine (AA)
- Serine can then make cysteine and glycine
Alpha-ketoglutarate (also in …) can be used to make
- Glutamate
- Glutamate can then make glutamine, proline, arginine
Phosphoenolpyruvate (also in …) + Erythrose-4-phosphate (also in …) can be used to make
- Phenylalanine (then tyrosine)
- Tyrosine
- Tryptophan
Cysteine is formed from
- Carbons from serine
- Sulfur from methionene
Glysine is formed from
- Serine by a serine hydroxymethyl transferase
Reversible transfer of the side chain carbon atom of serine to tetrahydrofolate forms
-glycine
Glycine is a pyridoxical phpsphate
Alanine is formed by
- Transamination of pyruvate
- Made from pyruvate in a single step
Alanine is the 2nd most abundant
- Amino acid in circulation
- (Number 1 is glutamine)
Alanine is important in the glucose-alanine cycle because it links
- Carbohydrate and amino acid metabolism
Alanine transaminase (ALT) serum levels are measured to
- Evaluate liver function
Alanine is a common substrate for gluconeogenesis by
- Reversal of this alanine formation via transamination of pyruvate reaction
Alanine transaminase (ALT) requires
- Pyridoxical cofactor
Alanine transaminase (ALT) requires
- Pyridoxical cofactor
Aspartate transaminas (AST) catalyzes
- Transamination of oxaloacetate to form aspartate
- Requires pyridoxical phopshate as a cofactor
Glutamate (alpha-ketoglutarate) participates in the aspartate transaminase reaction as the
- Amino group donor
Serum levels of AST are also utilized in
- Clinical evaluation of liver function
The amidation of aspartate is catalyzed by
- Asparagine synthetase
- Requires ATP
Nitrogen donor of aspartate amidation reaction
- Glutamine in eukaryotes
- Ammonium in bacteria
Glutamate dehydrogenase forms
- Glutamate from alpha ketoglutarate
- Reductive amination
- Reversible reaction
Hydroxyproline is formed from
- Proline catalyzed by a hydroxylase
- Requires molecular O2 and vitamin C
- Can be post-translationally modified
- Involved with collagen
Tyrosine (nonessential) is produced by
- Hydroxylation of phenylalanine (essential - from diet)
Tyrosine is not usually considered to be an essential amino acid when
- Phenylalanine is present in diet
Synthesized form ingested phenylalanine that is converted to tyrosine by
- Phenylalaine hydroxylase
Impossible to synthesize phenylalanine
- In the reverse direction
In PKU, a deficiency of the enzyme leads to
- Elevated phenylalanine levels in the blood
- Accumulation of
In the case of PKU, infants can be placed on
- Special diet
- Infants can alter diet again at 3-4 years of age and live a regular life
- Diagnosis must be made early
Phenylalanine is found in
- Aspartame
- Found in many artificial sweeteners
Interconversion of C1 units carried by
- Tetrahydrofolate in amino acid metabolism
Methyl-derivative is used to make
- Methionine (methionine synthase) is the most reduced
With vitamin B12 deficiency,
- Most THF is trapped in the methyl-derivative/form
- Manifests in pernicious anemia
Formyl derivative of THF is the most
- Oxidized form
When trapped in the methyl-form, there is a requirement for
- Vitamin B12
- Absorbtion requires intrinsic factor that is coming from parietal cells
In the absence of vitamin B12
- Methyl-form of THF cannot be removed or reused
- Causes circulation problems