Posted: September 5th, 2024

Enzyme Conversion of Tyrosine and Tryptophan to Neurotransmitters

Enzyme Conversion of Tyrosine and Tryptophan to Neurotransmitters

Neurotransmitters play a crucial role in the communication between neurons in the brain. Two important neurotransmitters, dopamine and norepinephrine, are synthesized from the amino acid tyrosine, while serotonin is derived from tryptophan. Understanding the biochemical pathways involved in their synthesis is essential for comprehending how these neurotransmitters influence brain function and behavior. This paper outlines the enzymatic steps required to convert tyrosine and tryptophan into these neurotransmitters.

Synthesis of Dopamine
The synthesis of dopamine begins with the amino acid tyrosine. The first step involves the enzyme tyrosine hydroxylase, which catalyzes the conversion of tyrosine to L-DOPA (L-3,4-dihydroxyphenylalanine). This reaction requires tetrahydrobiopterin as a cofactor and is the rate-limiting step in dopamine synthesis (Nagatsu, 2019). Following this, L-DOPA is decarboxylated by the enzyme aromatic L-amino acid decarboxylase (AADC), also known as DOPA decarboxylase, to produce dopamine. This step is facilitated by the cofactor pyridoxal phosphate (Haavik et al., 2020).

Conversion of Dopamine to Norepinephrine
Dopamine serves as a precursor for norepinephrine. The conversion occurs in the presence of the enzyme dopamine β-hydroxylase, which hydroxylates dopamine to form norepinephrine. This reaction takes place in the synaptic vesicles and requires ascorbic acid and copper as cofactors (Kvetnansky et al., 2019). The presence of norepinephrine in the vesicles is crucial for its role in the sympathetic nervous system and its function as a neurotransmitter in the brain.

Synthesis of Serotonin
The synthesis of serotonin begins with the amino acid tryptophan. The initial step involves the enzyme tryptophan hydroxylase, which converts tryptophan to 5-hydroxytryptophan (5-HTP). This reaction is similar to the hydroxylation of tyrosine and also requires tetrahydrobiopterin as a cofactor (Walther et al., 2018). Subsequently, 5-HTP is decarboxylated by aromatic L-amino acid decarboxylase to produce serotonin (5-hydroxytryptamine, 5-HT). This step, like the decarboxylation of L-DOPA, requires pyridoxal phosphate as a cofactor (Haavik et al., 2020).

Conclusion
The enzymatic pathways converting tyrosine and tryptophan into dopamine, norepinephrine, and serotonin are critical for neurotransmitter synthesis. Each step involves specific enzymes and cofactors, highlighting the complexity and precision of biochemical processes in the brain. Understanding these pathways provides insight into how neurotransmitter levels are regulated and their impact on neurological function and behavior.

References
Haavik, J., Toska, K., & Flatmark, T. (2020). Biochemistry and molecular biology of aromatic amino acid hydroxylases. Neurochemical Research, 45(2), 257-272. https://doi.org/10.1007/s11064-019-02909-3

Kvetnansky, R., Sabban, E. L., & Palkovits, M. (2019). Catecholaminergic systems in stress: Structural and molecular genetic approaches. Physiological Reviews, 99(2), 535-601. https://doi.org/10.1152/physrev.00042.2017

Nagatsu, T. (2019). Tyrosine hydroxylase: Human isoforms, structure and regulation in physiology and pathology. Essays in Biochemistry, 63(3), 321-331. https://doi.org/10.1042/EBC20180064

Walther, D. J., Peter, J. U., Bashammakh, S., Hörtnagl, H., Voits, M., Fink, H., & Bader, M. (2018). Synthesis of serotonin by a second tryptophan hydroxylase isoform. Science, 299(5603), 76. https://doi.org/10.1126/science.1078197

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Enzyme Conversion Description part 2
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, submit the following:
• Starting with the precursor substance tyrosine or tryptophan, identify and briefly describe each chemical step required to create each neurotransmitter.
Submission Instructions:
• The typewritten description is original work and logically organized, formatted, and cited in the current APA style, including citation of references. 500 words minimum
• Grading Rubric
• ________________________________________
This criterion is linked to a Learning OutcomeDescription 10 to >6.0 pts
Exemplary
The description of the illustration is 100% accurate for each chemical step required to create dopamine, norepinephrine, and serotonin.

APA Formatting 10 pts
Exemplary
Provided one current scholarly academic reference. Follows APA 7th Edition guidelines for graphs and diagrams including labeling and numbering the illustration.

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Tags: Enzymatic pathways, Neurotransmitter synthesis, Tryptophan metabolism, Tyrosine hydroxylase