Metabolism of phenylalanine and tyrosine

Summary

This script delves into the metabolism of the aromatic amino acids phenylalanine and tyrosine by liver cells, highlighting their conversion into acetyl acetate and fumarate. These compounds serve as precursors for ketone bodies and glucose, respectively, demonstrating the dual role of these amino acids as both gluconeogenic and ketogenic. The detailed enzymatic processes, including the function of phenylalanine hydroxylase and tyrosine amino transferase, are outlined, culminating in the formation of essential fuel molecules for the body.

Takeaways

• 🌟 Phenylalanine and tyrosine are aromatic amino acids that can be metabolized by liver cells to form acetyl acetate and fumarate.
• 🔍 Acetyl acetate is used for ketone body formation, while fumarate is used for glucose production, making these amino acids both glucogenic and ketogenic.
• 🧬 The first step in the process involves converting phenylalanine to tyrosine, catalyzed by the enzyme phenylalanine hydroxylase.
• 🌀 Phenylalanine hydroxylase is a mixed function oxygenase, utilizing diatomic oxygen to form tyrosine and water.
• 💧 The enzyme requires tetrahydrobiopterin for its activity, which is synthesized from dihydrobiopterin with the help of NADPH and dihydrofolate reductase.
• ♻️ Dihydropyridine reductase regenerates tetrahydrobiopterin, allowing for its reuse in the reaction.
• 🔄 Tyrosine amino transferase, using PLP (pyridoxal phosphate), transfers the alpha amino group from tyrosine to an alpha keto acid, forming p-hydroxyphenylpyruvate.
• 🌀 p-Hydroxyphenylpyruvate dioxygenase removes a carbon dioxide molecule and adds both atoms of diatomic oxygen to the substrate, forming homogentisate.
• 🔄 Another dioxygenase, homogentisate 1,2-dioxygenase, further modifies the molecule to form allyl acetyl acetate.
• 🔄 An isomerase, using glutathione, converts allyl acetyl acetate into fumarate and acetyl acetate.
• 🌿 The final step cleaves the bond in acetyl acetate to form fumarate and acetyl acetate, which can be used for glucose and ketone body synthesis, respectively.

Q & A

What are the two aromatic amino acids discussed in the script?

The two aromatic amino acids discussed in the script are phenylalanine and tyrosine.

How are phenylalanine and tyrosine related to glucose and ketone bodies?

Phenylalanine and tyrosine are known as glucogenic and ketogenic amino acids because they can be metabolized to form both glucose and ketone bodies.

What is the first step in the metabolic pathway of phenylalanine and tyrosine?

The first step is the transformation of phenylalanine into tyrosine, catalyzed by the enzyme phenylalanine hydroxylase.

What type of enzyme is phenylalanine hydroxylase?

Phenylalanine hydroxylase is a mixed function oxygenase, which uses a diatomic oxygen molecule for the reaction.

What is the role of tetrahydrobiopterin in the first step of the metabolic pathway?

Tetrahydrobiopterin provides the reducing power necessary for phenylalanine hydroxylase to catalyze the conversion of phenylalanine to tyrosine.

How is tetrahydrobiopterin synthesized in our cells?

Tetrahydrobiopterin is synthesized from dihydrobiopterin in the presence of NADPH and an H+ ion, catalyzed by the enzyme dihydrofolate reductase.

What is the purpose of the enzyme dihydropyridine reductase in this metabolic pathway?

Dihydropyridine reductase is used to regenerate tetrahydrobiopterin from its reduced form, using the reducing power of NADPH.

What enzyme is responsible for transferring the alpha amino group from tyrosine to an alpha keto acid?

The enzyme responsible for this transfer is tyrosine aminotransferase, which uses pyridoxal phosphate (PLP) for the reaction.

What intermediate is formed after the removal of carbon dioxide from the substrate molecule in the metabolic pathway?

The intermediate formed is homogentisate, after the carbon dioxide is removed and two oxygen atoms are attached to the substrate.

What type of enzyme is used to isomerize homogentisate to form fumarate and acetyl acetate?

An isomerase enzyme, specifically homogentisate isomerize, is used to isomerize homogentisate to form fumarate and acetyl acetate.

What is the final product of the metabolic pathway for phenylalanine and tyrosine?

The final products of the metabolic pathway are acetyl acetate and fumarate, which can be used to form ketone bodies and glucose, respectively.