<prompt> The rate-limiting step for norepinephrine synthesisConversion of phenylalanine to TyrosineConversion of Tyrosine to DOPAConversion of DOPA to dopamineConversion of dopamine to norepinephrine  <response>: In the synthesis of Norepinephrine, Tyrosine is hydroxylated to 3,4dihydroxyphenylalanine by tyrosine hydroxylase. This enzyme catalyses the rate limiting reaction and require tetrahydrobiopterin as coenzyme.Ref: Biochemistry, U. Satyanarayana, Fouh edition, page no: 349 