Amino Acids and Transamination Reactions

Questions and Answers

What is the primary function of amino acid metabolism in the human body?

To synthesize proteins, enzymes, hormones, and other important substances (correct)

To store amino acids for later use

To produce energy for the body

To break down fats and carbohydrates

What is the major organ responsible for transamination reactions in the human body?

Brain

Heart

Liver (correct)

Kidney

What is the coenzyme required for transaminase enzymes to catalyze transamination reactions?

Pyridoxal phosphate (PLP) (correct)

Thiamine

Niacin

Riboflavin

What is the percentage of amino nitrogen that is converted to urea and excreted from the body via urine?

95% Signup and view all the answers

What is the result of protein and amino acid catabolism in the human body?

Production of ammonia and urea Signup and view all the answers

What is the definition of transamination?

The transfer of amino groups from amino acids to ketoacids Signup and view all the answers

What is the purpose of transamination reactions in amino acid metabolism?

To remove amino nitrogen from the body Signup and view all the answers

What is the difference between transamination and deamination?

Transamination is the transfer of amino groups, while deamination is the removal of amino groups Signup and view all the answers

What are the exceptions for amino acids that undergo transamination reactions?

Lysine, threonine, proline, and hydroxyproline Signup and view all the answers

Where do most transamination reactions take place?

Cytosol and mitochondria of most tissues Signup and view all the answers

What is the function of ALT in the body?

To indicate liver inflammation Signup and view all the answers

What is the result of oxidative deamination?

Removal of an amino group and conversion to keto group with release of NH4 Signup and view all the answers

What is the main pathway by which amino group of most amino acids is released?

Transdeamination Signup and view all the answers

What is the function of γ-Amino butyric acid (GABA) in the body?

Neurotransmitter Signup and view all the answers

What happens to the resulting amines after carrying out their functions?

They are further oxidized by amine oxidase enzymes Signup and view all the answers

What is the purpose of glutamate transaminase?

To catalyze the transamination of glutamate to α-ketoglutarate Signup and view all the answers

Study Notes

Amino Acid Metabolism

Amino acid metabolism involves biochemical pathways that produce, break down, and use amino acids.
The body uses amino acids to make proteins, enzymes, hormones, and precursors to biogenic amines, hemoglobin, and genetic material (purines and pyrimidines).

General Catabolic Pathways of Amino Acids

Unlike fats and carbohydrates, there is no dedicated storage of proteins and amino acids in the human body.
The end products of protein and amino acid catabolism are ammonia and urea, produced through transamination, deamination, transdeamination, and decarboxylation.

Transamination

Transamination is the transfer of an amino group from an α-amino acid to an α-ketoacid, forming a new α-amino acid and a new α-ketoacid.
This reaction is catalyzed by enzymes called transaminases (or amino transferases) that require pyridoxal phosphate (PLP = active vitamin B6) as a coenzyme.
Transamination reactions are reversible and occur in the cytosol or both cytosol and mitochondria of most tissues.
Three transaminases (ALT, AST, and glutamate transaminase) are present in most mammalian tissues and are clinically important.
ALT is a more specific indicator of liver inflammation than AST due to its presence mainly in the liver.

Oxidative Deamination

Oxidative deamination is the removal of an amino group from a molecule, converting it to a keto group with simultaneous release of NH4.
This reaction is catalyzed by deaminases, mainly in the liver and kidney.
The resulting NH4+ enters the urea cycle, and α-ketoglutarate may be used in transamination or the Krebs cycle.

Transdeamination

Transdeamination is the transamination of most amino acids with α-ketoglutarate to form glutamate, which is then deaminated to give ammonia (NH3).
This is the main pathway by which the amino group (NH2) of most amino acids is released in the form of ammonia (NH3).

Decarboxylation

Decarboxylation is the removal of CO2 from amino acids, producing the corresponding amines.
Some amines have important biologic functions, such as histamine (a vasodilator) and γ-aminobutyric acid (a neurotransmitter).
The resulting amines are further oxidized by amine oxidase enzymes after carrying out their functions.