The rate-limiting step for nor-epinephrine synthesis is:
Conversion of phenylalanine to tyrosine
Conversion of tyrosine to DOPA
Conversion of DOPA to dopamine
Conversion of dopamine to norepinephrine
Ref: KD Tripathi Pharmacology 7th edition(page no;125) Catecholamines like epinephrine, norepinephrine, dopamine are synthesized from the amino acid phenylalanine. Tyrosine hydroxylase is the rate-limiting enzyme and its inhibition by alpha-methyl-p-tyrosine results in depletion of norepinephrine Tyrosine hydroxylase helps in Conversion of tyrosine to DOPA
Autonomic nervous system