amino acid metabolism
TRANSCRIPT
AMINO ACID METABOLISM
BY MUHAMMAD HASEEB TARIQ
PROTEINS
Proteins are formed of repeating units of Amino acids.
Half of the body protein (collagen) is present in supportive tissue.
Other half is present Intracellularly.
GENERAL CLASSIFICATION
Amino Acids are classified in 3 categories:• Essential (Can’t be synthesized in body)• Non-Essential (Can be synthesized in body)• Semi-Essential
Total amino acids are 20.Essential amino acids are 10.
AMINO ACID POOL
Body contains 100g of protein present freely inside the body. This is amino acid pool.
Amino acids of pool are in dynamic state.These participate in different metabolic reactions
occurring in the body.CONTENTS:50% of the pool is formed of :• Glutamate • Glutamine.10% of pool is formed of Essential amino acids.
SOURCES:• Protein turnover• Ingestion
PROTEIN TURNOVER:The amount of protein degraded and
synthesized constantly in the body is called as protein turnover (300-400g).
Factors: • Ubiquitin tags a protein and increase its
degradation.• Amino acid sequence of Proline , Glutamine ,
Serine and Threonine increases the degradation.
Above factors are responsible for affecting Protein turnover.
INGESTION:• 30-50g protein is daily lost.• RDA for proteins is 1g/kg body weight/day.• Excess amino acids are not stored in body.
GENRAL ASPECTS OF AMINO ACID METABOLISM
Amino acids undergo 2 steps along metabolism. These are:
• Transamination• Deamination
TRANSAMINATIONDefinition:The transfer of an amino group (-NH2 ) from an
amino acid to a keto acid is known as Transamination.
Features:• The reaction is catalysed by transaminases.• All reactions require PLP derivative of B6.
• No free NH3 is liberated, just transfer occurs.
• Excess amino acids are diverted to generate energy.
• Nitrogen is finally concentrated in Glutamate.• Only Glutamate undergoes oxidative
deamination to liberate ammonia.• Serum transaminases can be used for
diagnostic and prognostic purposes.
MECHANISM OF TRANSAMINATIONPING PONG BI BI MODEL:
• Amino group is transferred to Pyridoxal phosphate converting it to Pyridoxamine phosphate.
• Amino group is transferred to a keto acid converting Pyridoxamine phosphate to Pyridoxal phosphate.
• During the reactions there is formation of Schiff base.
DEAMINATION
Definition:The removal of amino group as NH3 is called as
Deamination.
Mostly it occurs in:• Liver• Kidneys
Deamination is of 2 types:• Oxidative deamination (coupled with
oxidation)• Non-oxidative deamination
OXIDATIVE DEAMINATIONGlutamate acts as a collection centre for amino
groups.Deamination requires enzyme Glutamate
Dehydrogenase (GDH).It is inhibited by ATP, GTP and allosterically
activated by ADP, GDP.Amino acid oxidases can also cause deamination.GDH:Zn containing enzyme.6 identical subunits. Molecular wt. 56000 each.
EFFECT OF PROTEIN RICH MEAL:After ingestion of protein rich meal glutamate
level is increased, which leads to increased levels of NH3 in body.
AMINO ACID OXIDASES:These are flavo proteins, possessing FMN and
FAD.Activity of L-amino acid oxidases is low than D-
amino acid oxidases.Hydrogen peroxide is produced in these
reactions which is then acted upon by Catalase.
NON-OXIDATIVE DEAMINATIONFollowing enzymes cause it :• Dehydratase (acts on Serine, Threonine ,
Homoserine)• Desulfhydrases (acts on Cystein ,
Homocystein)• Histidase (acts on histidine)
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