Amino Acid Nitrogen Removal and Urea Cycle Formulas

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26 Questions

Which of the following amino acids is NOT capable of undergoing transamination?

Glutamine

Which enzyme is specific and presents clinical diagnostic importance due to its presence in most tissues?

Alanine transaminase (ALT, or GPT)

Which coenzyme is required for transaminases to catalyze transamination reactions?

Pyridoxal phosphate (PLP)

Where does transamination mainly occur?

Liver, kidney, brain, and heart

Which process involves the reversible transfer of an amino group from an α-amino acid to an α-keto acid?

Transamination

Which enzyme catalyzes the transfer of amino group from aspartate to α-ketoglutarate to form glutamate and oxaloacetate?

Aspartate transaminase (AST)

What is the normal plasma level of Alanine transaminase (ALT) or glutamate-pyruvate transaminase (GPT)?

0 - 42 IU/L

Which type of deamination involves the removal of hydrogen sulfide (H2S)?

Desulfhydrase

What is the specific function of D-amino acid oxidase?

Acts on unnatural D-amino acids

What is transamination?

Transamination is the reversible transfer of an amino group from an α-amino acid to an α-keto acid, forming a new α-amino acid and a new α-keto acid.

Which enzyme allows the transfer of hydrogen from the L-amino acid to molecular O2 with formation of H2O2?

L-amino acid oxidase

What are the three specific transaminases with clinical diagnostic importance?

The three specific transaminases with clinical diagnostic importance are alanine transaminase (ALT, or GPT), aspartate transaminase (AST, or GOT), and glutamate transaminase.

Where does transamination mainly occur?

Transamination mainly occurs in the liver, kidney, brain, and heart.

What is the diagnostic importance of transaminases?

Transaminases have clinical diagnostic importance and can be used for diagnostic purposes.

What is the function of transaminases or aminotransferases?

Transaminases or aminotransferases catalyze the transamination reactions.

What is the normal plasma level for Alanine transaminase (ALT) or glutamate-pyruvate transaminase (GPT)?

0 - 42 IU/L

Which amino acids are not transaminable?

Lysine, threonine, proline, and hydroxyproline are not transaminable.

Where is Aspartate transaminase (AST) present?

Both cytosol and mitochondria of myocardium, liver mainly but also of muscles, pancreas, kidney, etc.

What is the site for 2-Deamination, the removal of amino groups from amino acids as free ammonia (NH3)?

Mostly liver and kidney

Name the three oxidative deaminases involved in the reversible removal of the amino group as ammonia secondary to dehydrogenation of the amino acid.

L-amino acid oxidase, D-amino acid oxidase, L-glutamate dehydrogenase

What is the specific function of L-amino acid oxidase?

It is specific for the natural isomers of amino acids, i.e., L-amino acids but does not act on glycine, acidic, basic or β-hydroxy amino acids.

What type of deamination involves the addition of water?

Hydrolytic deamination

Which enzyme catalyzes the transfer of amino group from aspartate to α-ketoglutarate to form glutamate and oxaloacetate?

Aspartate transaminase (AST) or glutamate-oxaloacetate transaminase (GOT)

Name the type of deamination combined with removal of hydrogen sulfide (H2S).

Desulfhydrase

What is the reversible removal of the amino group as ammonia secondary to dehydrogenation of the amino acid called?

Oxidative deamination

What is the coenzyme required for transaminases to catalyze transamination reactions?

Pyridoxal phosphate (PLP)

Study Notes

Amino Acid Metabolism

  • Proline is not capable of undergoing transamination.
  • Aspartate transaminase (AST) is an enzyme specific to most tissues and has clinical diagnostic importance.
  • The coenzyme required for transaminases to catalyze transamination reactions is Pyridoxal phosphate (PLP).
  • Transamination mainly occurs in the liver and kidneys.

Transamination Reaction

  • Transamination involves the reversible transfer of an amino group from an α-amino acid to an α-keto acid.
  • The enzyme that catalyzes the transfer of an amino group from aspartate to α-ketoglutarate to form glutamate and oxaloacetate is aspartate transaminase (AST).

Diagnostic Importance

  • The normal plasma level of Alanine transaminase (ALT) or glutamate-pyruvate transaminase (GPT) is 0-40 IU/L.
  • Transaminases have clinical diagnostic importance due to their presence in most tissues.

Deamination

  • Desulfhydration is a type of deamination that involves the removal of hydrogen sulfide (H2S).
  • The specific function of D-amino acid oxidase is to catalyze the deamination of D-amino acids.
  • L-amino acid oxidase is the enzyme that allows the transfer of hydrogen from the L-amino acid to molecular O2 with formation of H2O2.
  • The site for 2-Deamination, the removal of amino groups from amino acids as free ammonia (NH3), is the liver.
  • The three oxidative deaminases involved in the reversible removal of the amino group as ammonia secondary to dehydrogenation of the amino acid are L-amino acid oxidase, D-amino acid oxidase, and Glutamate dehydrogenase.

Transaminases

  • The function of transaminases or aminotransferases is to catalyze transamination reactions.
  • The three specific transaminases with clinical diagnostic importance are Aspartate transaminase (AST), Alanine transaminase (ALT), and Glutamate-pyruvate transaminase (GPT).
  • The amino acids that are not transaminable are Proline and Hydroxyproline.

Test your understanding of the removal and fate of amino acid nitrogen, urea cycle reactions, metabolic importance of transamination, sources and mechanism of ammonia intoxication, steps and regulation of urea cycle, and urea cycle defects. This quiz focuses on names and formulas for understanding only.

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