Question

Both norepinephrine and epinephrine are synthesized from the same protein- derived amino acid. From which amino acid are they synthesized, and what types of reactions are involved in their biosynthesis? a. b.

Short answer

Answer: Norepinephrine and epinephrine are synthesized from the amino acid tyrosine. The types of reactions involved in their biosynthesis include hydroxylation, decarboxylation, and methylation.

Step-by-step solution

Identify the amino acid from which norepinephrine and epinephrine are synthesized

Norepinephrine and epinephrine are both synthesized from the same protein-derived amino acid, which is tyrosine.

Discuss the types of reactions involved in their biosynthesis

The biosynthesis of norepinephrine and epinephrine involves several enzyme-catalyzed reactions. These reactions include the following: a. Hydroxylation of tyrosine: In the first step, tyrosine is hydroxylated to form dihydroxyphenylalanine (DOPA) by the enzyme tyrosine hydroxylase. The reaction is as follows: \[ \text{Tyrosine} + \text{O}_2 + \text{BH}_4 \rightarrow \text{DOPA} + \text{H}_2\text{O} + \text{BH}_2 \] b. Decarboxylation of DOPA: In the second step, DOPA is decarboxylated to form dopamine by the enzyme DOPA decarboxylase. The reaction is as follows: \[ \text{DOPA} \rightarrow \text{Dopamine} + \text{CO}_2 \] c. Hydroxylation of dopamine: In the third step, dopamine is hydroxylated to form norepinephrine by the enzyme dopamine β-hydroxylase. The reaction is as follows: \[ \text{Dopamine} + \text{O}_2 + \text{ascorbate} \rightarrow \text{Norepinephrine} + \text{H}_2\text{O} + \text{dehydroascorbate} \] d. Methylation of norepinephrine: In the last step, norepinephrine is methylated to form epinephrine by the enzyme phenylethanolamine N-methyltransferase (PNMT). The reaction is as follows: \[ \text{Norepinephrine} + \text{S-adenosylmethionine} \rightarrow \text{Epinephrine} + \text{S-adenosylhomocysteine} \] In summary, norepinephrine and epinephrine are synthesized from the amino acid tyrosine through a series of enzyme-catalyzed reactions, including hydroxylation, decarboxylation, and methylation.

Key concepts

Tyrosine

Tyrosine is a key amino acid involved in the biosynthesis of important hormones and neurotransmitters in the body. Its chemical structure provides the foundation for producing norepinephrine and epinephrine, two critical catecholamines. These molecules have powerful effects on the body, such as regulating heart rate and blood pressure. Tyrosine is derived from another amino acid called phenylalanine, which is obtained directly from dietary sources. During the biosynthesis of norepinephrine and epinephrine, tyrosine undergoes specific modifications through enzyme-catalyzed reactions, altering its structure to form these potent biological molecules. Its role is essential, serving as the primary building block in this metabolic pathway.
A varied diet containing tyrosine and phenylalanine ensures the body has sufficient resources to produce norepinephrine and epinephrine when needed. Thus, understanding tyrosine's essential role sheds light on the dietary considerations necessary for maintaining hormonal balance and nerve function.

Enzyme-Catalyzed Reactions

Enzyme-catalyzed reactions are biochemical reactions facilitated by enzymes, which are proteins that act as catalysts in the body. These enzymes speed up chemical reactions without being consumed in the process. This efficiency plays a crucial role in the biosynthesis of norepinephrine and epinephrine from tyrosine. Each step in this pathway is tightly controlled by a specific enzyme that performs its function under particular conditions.
In the biosynthesis, enzymes such as tyrosine hydroxylase, DOPA decarboxylase, and dopamine β-hydroxylase specifically act on intermediates like DOPA and dopamine. By doing so, they ensure that the pathway progresses rapidly and accurately to end products like norepinephrine and epinephrine. These enzymes lower the energy requirements for these modifications to take place, making it feasible for the body to produce necessary neurotransmitters under varying physiological conditions. Understanding enzyme function is crucial for comprehending how metabolic pathways are regulated and maintained.

Hydroxylation

Hydroxylation is a chemical process in which a hydroxyl group (-OH) is added to an organic compound. This step is integral to the pathway where tyrosine is transformed into norepinephrine and epinephrine. The hydroxylation reaction is performed by the enzyme tyrosine hydroxylase, which converts tyrosine into dihydroxyphenylalanine (DOPA). This step requires oxygen ( O_2 ) as a reactant and involves the cofactor tetrahydrobiopterin (BH_4), which is essential for the enzyme's activity.
Hydroxylation increases the molecule's ability to participate in further enzymatic reactions, setting the stage for subsequent conversions in the biosynthetic pathway. Hydroxyl groups are reactive and often participate in hydrogen bonding, critical for the molecule's solubility and reactivity, highlighting the importance of this modification in transforming tyrosine into vital neurotransmitters.

Decarboxylation

Decarboxylation is a process that involves the removal of a carboxyl group ( CO_2 ) from organic molecules such as amino acids. In the biosynthesis pathway of norepinephrine and epinephrine, the decarboxylation step is catalyzed by the enzyme DOPA decarboxylase, which converts DOPA into dopamine. This reaction is crucial because it alters the chemical nature of the substrate, paving the way for its transformation into neurotransmitters.
This step helps in reducing the size of the molecule and changes its chemical properties, allowing it to fit perfectly into subsequent enzymatic reactions. It illustrates how slight modifications can lead to the creation of biologically active compounds from relatively simple precursors like tyrosine. Understanding decarboxylation helps us unravel how complex chemicals in the body are assembled from basic building blocks.

Methylation

Methylation is the process of adding a methyl group (CH3) to a molecule. In the biosynthesis of epinephrine, methylation is the final step. This reaction is facilitated by the enzyme phenylethanolamine N-methyltransferase (PNMT), which transfers a methyl group from S-adenosylmethionine (SAM) to norepinephrine, resulting in the synthesis of epinephrine. This modification notably changes the hormone's function and properties.
Methylation is a crucial reaction in biochemistry, serving not only in hormone synthesis but also influencing gene expression and DNA repair. The alteration brought by methylation significantly impacts the biological activity and solubility of molecules, making it indispensable for producing functionally diverse compounds critical for various physiological roles. By comprehending methylation's role in epinephrine synthesis, we gain insight into how biochemical diversity is generated from basic enzymatic steps.