<prompt> Post-translational modification of hydroxylases is mediated byVitamin KVitamin EVitamin CVitamin D  <response>: Ascorbic acid has specific roles in the copper-containing hydroxylases and the a-ketoglutarate-linked iron-containing hydroxylases. Dopamine b-hydroxylase is a copper-containing enzyme involved in the synthesis of the catecholamines norepinephrine and epinephrine, from tyrosine in the adrenal medulla and central nervous system. During hydroxylation the Cu is oxidized to Cu2; reduction back to Cu specifically requires ascorbate, which is oxidized to monodehydroascorbate. Reference: Harper; 30th edition; Page no: 561 