STAGES OF AMINO ACIDS CATABOLISM

Dr. Samah KotbLecturer of Biochemistry

2015

Cellular Biochemistry and metabolism 2

CLS 333

STAGES OF AMINO ACIDS CATABOLISM

CHAPTER 8

• Amino acids are the building blocks of the proteins.

• Twenty amino acids are commonly found in proteins.

INTRODUCTION

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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.

INTRODUCTION

• 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

• 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.

Catabolism of Amino Acids in Animal Tissue

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

Stages of Amino Acids CatabolismStages 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:

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Stage 2: Oxidation of Ketoacids:

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Stage 2: Oxidation of Ketoacids:

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Stage 2: Oxidation of Ketoacids:

Oxidation of ketoacids of corresponding amino acids