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