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Enzyme Conversion Description

After studying Module 2: Lecture Materials & Resources, submit the following:

  • Starting with the precursor substance tyrosine or tryptophan, identify and briefly describe each chemical step required to create each neurotransmitter. 

Expert Solution Preview

Introduction:
Creating assignments and providing answers for medical college students is a crucial task in the role of a medical professor. In this case, the assignment focuses on the enzymatic conversion of precursor substances into neurotransmitters. Precursor substances, such as tyrosine or tryptophan, undergo specific chemical steps to form various neurotransmitters. Let’s explore the process involved in the synthesis of neurotransmitters from these precursor substances.

Answer:
1. Tyrosine to Dopamine:
Tyrosine is first converted into L-DOPA through the action of the enzyme tyrosine hydroxylase. This conversion involves the hydroxylation of the aromatic ring of tyrosine. The enzyme requires tetrahydrobiopterin (BH4) as a cofactor.

Next, L-DOPA is decarboxylated by the enzyme aromatic L-amino acid decarboxylase (AADC) to form dopamine. This reaction removes the carboxyl group from the L-DOPA molecule.

2. Tyrosine to Norepinephrine and Epinephrine:
After the formation of dopamine, it can be further converted into norepinephrine and epinephrine. The conversion of dopamine to norepinephrine involves the enzyme dopamine beta-hydroxylase, which adds a hydroxyl group to the β-carbon of dopamine.

Norepinephrine can either be stored and utilized as a neurotransmitter or can be further converted to epinephrine. The conversion of norepinephrine to epinephrine requires the enzyme phenylethanolamine-N-methyltransferase (PNMT). This enzyme transfers a methyl group from S-adenosyl methionine (SAM) to the oxygen atom of norepinephrine, resulting in the formation of epinephrine.

3. Tryptophan to Serotonin:
Tryptophan is first hydroxylated by the enzyme tryptophan hydroxylase. This enzyme adds a hydroxyl group to the 5th position of tryptophan, forming 5-hydroxytryptophan (5-HTP).

Next, 5-HTP is decarboxylated by the enzyme aromatic L-amino acid decarboxylase (AADC) to form serotonin. This decarboxylation step removes the carboxyl group from 5-HTP.

These chemical steps represent the enzymatic conversions involved in the synthesis of neurotransmitters from the precursor substances tyrosine and tryptophan. The precise regulation and activity of the specific enzymes involved in these conversions play a crucial role in maintaining neurotransmitter balance and function within the central nervous system.