<prompt> The rate-limiting step for nor-epinephrine synthesis is:Conversion of phenylalanine to tyrosineConversion of tyrosine to DOPAConversion of DOPA to dopamineConversion of dopamine to norepinephrine  <response>: Ref: KD Tripathi Pharmacology 7th editionpage 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 