Abstract

Dopamine β-hydroxylase (EC 1.14.2.1) from tissue homogenates of three species was subjected to electrophoresis on polyacrylamide gel and starch blocks. In both systems dopamine β-hydroxylase in crude homogenates of solid tissues exhibited two electrophoretically distinguishable peaks of activity. The smaller, more slowly migrating peak was eliminated by high-speed centrifugation prior to electrophoresis, suggesting that this peak represented a form of the enzyme bound to the membrane or to a subcellular constituent. This interpretation is supported by partial conversion of dopamine β-hydroxylase activity from the slowly moving peak to the fast-migrating peak by Triton treatment. Also in harmony with this view are the observations that a nonparticulate tissue such as serum contained only the faster-migrating peak and that prior treatment with reserpine produced elevations of both peaks in solid tissues. The main peak of dopamine β-hydroxylase activity from human, cow, and rat adrenals differed in electrophoretic mobility, but within each species the major peak of activity from all tissues, including serum, had the same mobility. Human serum dopamine β-hydroxylase activity migrated with the mobility of a β-globulin. The major peak of enzyme activity from each species was broad and asymmetrical, and possibly included several distinct molecular forms of the enzyme.