Ans: See Handout # 5 under "Drugs Acting on Catecholamine Synthesis" for the structures of a-methyltyrosine and a-methyldopa. It should be apparent that a-methyltyrosine will compete with the substrate L-tyrosine for tyrosine hydroxylase due to its structural similarity while a-methyldopa will compete with L-Dopa for the enzyme L-aromatic amino acid decarboxylase. Thus, both of these compounds are effective inhibitors for the biosynthesis of dopamine (i.e., at the dopaminergic neurons) as well as norepinephrine (at the adrenergic synapses).