Download Generalities Main amino acid reactions

Generalities
 Proteins are the polypeptides formed by sequences
of amino acids
 General formula of the a-amino acids
NH2-CH-COOH
R
 The amino acids occupy a central position in the
metabolism of nitrogenous compounds
Main amino acid reactions
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TRANSAMINATION
DEAMINATION
DECARBOXYLATION
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The degradation of the amino acids occurs in the mitochondria.
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By a transamination reaction (1) the amino group is transferred to aketoglutarate to form glutamate in a reversible way.
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Glutamate release ammonia through an oxidation reaction
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Most amino acids have their specific transaminase, and those that do not
have can be transformed into other that has.
(1) Transaminations are reactions involved in both, anabolism and catabolism.
1
 Transamination reaction
COO CHNH2
R
COO CO
R
PLP
COO CO
CH2
CH2
COO aKG
COO CHNH2
CH2
CH2
COO Glu
 Reaction : transamination
(exchange of amine group)
 Enzyme: transaminase
(aminotransferase) in cytosol
 Coenzyme activateur:
Pyridoxal Phosphate (PLP)
 Reversible
Pyridoxal phosphate (PLP)
H
HO
C
NH2
H C H
HO
CH2 OP
O
N
CH2 OP
N
CH3
Pyridoxal phosphate
(PLP)
COO CO
R
PLP
Glu
CH3
Pyridoxamine phosphate
(PMP)
Mechanisme
COO CHNH2
R
Coenzyme associated
with numerous
enzymes acting on
nitrogen compounds
- transaminases
- isomerase
- decarboxylase...
PMP
a KG
 Ping–pong reaction:
1 - fixation of the substrate 1 to the
active site of the enzyme, then
formation of the product which is
detached from the active site
2 - fixation of the substrate 2 to the
active site of the enzyme
2
 Oxidative deamination
 Elimination of nitrogenous from glutamate
H2 N CH COO - NAD+
CH2
CH2
COOH
H2 O
NADH
O C COO
CH2
CH2
COOH
NH4 +
 Transformation of glutamate (formed by protein degradation or
by AA transamination) in α-ketoglutarate and NH4+
 Oxidation coupled to hydrolysis
 Enzyme: Dehydrogenase (Glutamate dehydrogenase)
 Amoniac fate
 Stored as glutamine
NH4 +
H2 N CH COOH
H2 N
CH2
CH2
C O
ATP
ADP + P
OH
CH COOH
CH2
CH2
C O
NH2
Glutamine synthétase
 Coupled reaction: hydrolysis of ATP and condensation of
NH4+ on glutamate (double transfer)
 Elimination by urea cycle
3
Lateral chain degradation
 In general, N elimination occurs by transamination, then
CO2 is liberated by an oxidative decarboxylation :
- Formed a-ketoacides are Krebs or glycolysis
intermediates : pyruvate, a-ketoglutarate, OAA…
Example
(LipSS, TPP, FAD)
aKG
COOH
CHNH2
NAD+
Glu
(PLP)
CH3
COOH
CO
CH3
Transaminase
NADH
CH3 COSCoA
HSCoA CO2
Déshydrogénase
Aminoacids catabolism and anabolism are linked to
glycolysis and Krebs intermediates
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