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.

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

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.