Abstract

Dopamine β-hydroxylase (EC 1.14.17.1) was isolated as a pure protein from a human pheochromocytoma. The tumor enzyme has chemical and physical properties similar to those of the enzyme isolated from bovine adrenal medulla. Both enzymes are glycoproteins and have similar amino acid compositions. Both enzymes have subunit molecular weights of 75,000-77,000 determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis and by equilibrium centrifugation in 6 M guanidine hydrochloride after reduction and carboxymethylation. Equilibrium centrifugation in the presence of 6 M guanidine hydrochloride in the absence of reducing agents gives subunit molecular weights of about 150,000 for both enzymes. Studies of the native enzyme obtained from the human tumor show that, in contrast to the bovine enzyme, human dopamine β-hydroxylase has an unusual tendency to dissociate and aggregate; however, its behavior on Sephadex G-200 suggests a molecular weight of 300,000, the same as that of the bovine enzyme.