Ascorbate 2-sulfate inhibits dopamine beta-hydroxylase reaction, but not ascorbate oxidase reaction

Bovine adrenal dopamine beta-hydroxylase [EC 1.14.17.1] was considerably inhibited by ascorbate 2-sulfate. The inhibition was competitive with regard to ascorbate. The Ki value was 3.44 mM. The possibility that ascorbate 2-sulfate may play a regulatory role in the biosynthesis of norepinephrine is suggested. Another copper-containing oxidase, squash ascorbate oxidase [EC 1.10.3.3], was not inhibited by the same compound at a concentration of 150 mM.