STAGES OF AMINO ACIDS
CATABOLISM
Cellular Biochemistry and
metabolism 2
CLS 333
Dr. Samah Kotb
Lecturer of Biochemistry
2015
CHAPTER 8
STAGES OF AMINO ACIDS CATABOLISM
INTRODUCTION
• Amino acids are the building blocks of the proteins.
• Twenty amino acids are commonly found in proteins.
• Amino acids are essentially α-amino acids:
4
INTRODUCTION

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.
Essential Amino Acids
•
•
•
•
•
Arginine (Arg)
Threonine (Thr)
Lysine (Lys)
Valine (Val)
Phenylalanine (Phe)
•
•
•
•
•
Tryptophan (Trp)
Methionine (Met)
Histidine (His)
Leucine (Leu)
Isoleucine (Ile)
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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.
Catabolism of Amino Acids in Animal Tissue
• 20 amino acids catabolism give 10 % of daily energy
requirements.
Stages of Amino Acids Catabolism
There are 2 stages of amino acid catabolism:STAGE 1:
Removal
of
enzymatically
the
primary
catalyzed
amino
reaction
groups
by
known
an
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
Amino Acids
Stages
ofofAmino
AcidsCatabolism
Catabolism
Stage 1: TRANSAMINATION (Deamination)
The α amino group of the amino acid is enzymatically
transferred to an acceptor molecule namely αketoglutarate 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:-
Ammonia is formed from Glutamate
(Fate of Glutamate):
 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).
Stage 2: Oxidation of Ketoacids
 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.
Examples of oxidation of Ketoacids:
1.
Stage 2: Oxidation of Ketoacids:
2.
Stage 2: Oxidation of Ketoacids:
3.
Stage 2: Oxidation of Ketoacids:
4.
Oxidation of ketoacids of corresponding
amino acids