<prompt> The rate-limiting enzyme in the synthesis of dopamine is which of the following?Tyrosine hydroxylaseDopa decarboxylaseHomovanillic acidDopamine beta-hydroxylase  <response>: The first step in the chemical synthesis of dopamine, epinephrine, and norepinephrine is the conversion of L-tyrosine to L-hydroxyphenylalanine, which is catalyzed by tyrosine hydroxylase. This is the rate-limiting step. 