_______ is responsible for epinephrine production.

• A. Phenylethanolamine N-methyltransferase (PNMT)
• B. Tyrosine hydroxylase
• C. Dopamine beta-hydroxylase
• D. Monoamine oxidase

Answer: (A)

The final step in making epinephrine is the methylation of norepinephrine to epinephrine, and this is done by phenylethanolamine N-methyltransferase (PNMT). In the adrenal medulla, norepinephrine produced from dopamine is converted to epinephrine by PNMT. This enzyme is upregulated by cortisol from the adrenal cortex, which explains why the body increases epinephrine production under stress. The earlier steps—tyrosine hydroxylase turning tyrosine into DOPA, DOPA decarboxylase making dopamine, and dopamine beta-hydroxylase converting dopamine to norepinephrine—set up substrates for PNMT, but do not finalize epinephrine production. Monoamine oxidase, meanwhile, degrades monoamines rather than synthesizing epinephrine.