Cellular Biochemistry and Metabolism
(CLS 333 )
Dr. Samah Kotb Nasr Eldeen
STAGES OF AMINO ACIDS CATABOLISM
CHAPTER 8
INTRODUCTION
Amino acids are the building blocks of the proteins.
Twenty amino acids are commonly found in proteins.
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• Amino acids are essentially α-amino acids:
They differ from each other in their
side chains, or R groups, which vary in
structure, size, and electric charge, and
which influence the solubility of the
amino acids in water.
Arginine (Arg) Threonine (Thr) Lysine (Lys) Valine (Val) Phenylalanine
(Phe)
Tryptophan (Trp) Methionine (Met) Histidine (His) Leucine (Leu) Isoleucine (Ile)
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Essential Amino Acids
Catabolism of Amino Acids in Animal Tissue
Only 10 % of the daily energy requirements
of an average adult are provided by amino
acid degradation.
This is not high when compared to
monosaccharide (50%) and fatty acids (40%).
Catabolism of Amino Acids in Animal Tissue
Amino acids entering cells are
primarily used by the cells for
synthesize of various structurally or
biologically important proteins such as
enzymes and hormones.
Catabolism of Amino Acids in Animal Tissue
The remaining amounts of amino acids
after sufficient proteins have been
synthesized are now degraded to produce
energy equal to 10 % of the daily
requirements.
20 amino acids catabolism give 10 % of
daily energy requirements.
There are 2 stages of amino acid
catabolism:-
STAGE 1:
Removal of the primary amino groups by
an enzymatically catalyzed reaction known
as TRANSAMINATION catalyzed by enzymes
known as TRANSAMINASES.
Stages of Amino Acids Catabolism
STAGE 2:
Degradation of the remaining keto-acids
into acetyl-Co A or other TCA cycle
intermediates.
Stages of Amino Acids Catabolism
The α amino group of the amino acid is
enzymatically transferred to an acceptor
molecule namely α-ketoglutarate leaving
behind the corresponding keto acid. α-
ketoglutarate becomes aminated and
yields glutamate:-
Stage 1: TRANSAMINATION (Deamination)
Stage 1: TRANSAMINATION (Deamination)
α-ketoglutarate serves as the universal
acceptor of amino groups during the
transamination of all 20 amino acids.
However a specific transaminase is
required for each of the 20 amino acids.
Eg:-
Stage 1: TRANSAMINATION (Deamination)
Glutamate undergoes oxidative
deamination to remove the amino groups
which appears as ammonia.
The reaction is catalyzed by the enzyme
Glutamate Dehydrogenase which uses
NAD+ as a coenzyme. (a mitochondrial
enzyme).
Ammonia is formed from Glutamate (Fate of Glutamate):
As a result of transamination 20 different
ketoacids are formed.
Each of the 20 ketoacids is oxidized by a
specific pathway and end up as either acetyl-
CoA or one of the TCA cycle intermediates.
Some of these oxidative pathways are simple,
whereas others are complex & multistep.
Stage 2: Oxidation of Ketoacids
1.
Examples of oxidation of Ketoacids:
2.
Stage 2: Oxidation of Ketoacids:
3.
Stage 2: Oxidation of Ketoacids:
4.
Stage 2: Oxidation of Ketoacids:
Oxidation of ketoacids of corresponding amino acids