Dopamine β‐Monooxygenase

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Abstract
The binding of 64Cu to the water-soluble form of dopamine .beta.-monooxygenase [catalyzes hydroxylation of dopamine to norepinephrine] from bovine adrenal medulla was studied in reconstitution and exchange experiments using high-performance size-exclusion gel chromatography. The reconstitution experiments provide evidence for a specific binding of 4 Cu atoms/enzyme tetramer using either Cu(I) or Cu(II), but some weaker Cu-binding sites were observed in the presence of a large excess of Cu. The exchanges of both Cu(I) and Cu(II) in this protein are so rapid that exact half-lives for the exchange reactions can not be obtained by the present method. The half-life for the exchange of the enzyme-bound Cu in the holoenzyme with a 2-fold excess of 64Cu(II) at pH 6.1 was about 1 min, while the exchange of Cu(I) measured at similar conditions with ascorbate present, was complete in 1 min. This is by far the most rapid exchange reported for any Cu-protein, and the results point to a unique Cu-binding site in this enzyme.

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