Subunit characterization and primary structure of bovine adrenal medullary dopamine beta-hydroxylase

Bovine adrenal medullary dopamine beta-hydroxylase was purified by sucrose density sedimentation, gel filtration chromatography, and Concanavalin A-Sepharose 4B affinity chromatography. Three subunits have been identified, of 71, 75, and 78 kd, present at a ratio of 1:2:1. Homogeneous subunits were isolated on denaturing polyacrylamide gels. Endoglycosidase treatment reduced each polypeptide to a 66-kd species, indicating that high and complex mannans account for the major differences in the subunits. The subunits and their 66-kd products cross-react with an anti-native dopamine beta-hydroxylase antiserum, suggesting common antigenic epitopes. Amino acid content analysis shows enrichment in glutamic acid/glutamine, aspartic acid/asparagine, glycine, and leucine, with little cysteine, tyrosine, proline, lysine, and methionine. Two to three nonidentical polypeptides have been identified from cyanogen bromide fragments. Comparison of the bovine peptide sequences to the corresponding cDNA-deduced human sequences show substantial similarity. Many of the species-specific differences in the primary structure represent conservative changes in amino acids or single base pair changes in amino acid codons.