The Jourkal of Biowgical Chemistry

The enzyme dopaminel @-hydroxylase, which catalyzes the conversion of dopamine to norepinephrine, has been partially purified from beef adrenal medulla (1). The enzyme requires ascorbic acid and fumaric acid as cofactors (1). Without ascorbic acid a catechol compound can serve as an alternative reducing agent (2). The stimulation of dopamine hydroxylation by adenosine triphosphate and by catalase has been shown to be due to an effect. of these substances on enzyme stability (2). The enzyme is nonspecific and accepts a variety of substrates, including phenylethylamine, tyramine, epinine, 3-methoxydopamine, and other phenylethyland phenylpropylamines (2-6). Some compounds structurally related to dopamine, which are not substrates for the enzyme, act, as inhibitors (7, 8). The present report describes a method for the further purification of dopamine P-hydroxylase. Studies are reported on the inhibition of dopamine /3-hydroxylase by chelating agents which indicate that a metal ion is essential for the enzymatic activity. The role of catalase in protecting the enzyme from inactivation has been further elucidated. The effects of nucleotides on the enzymatic activity have been investigated with enzyme preparations at different purification stages. Preliminary reports on the inhibition of dopamine P-hydroxylase by chelating agents were published by us (9-11) and by others (12).