Deglycosylated membranous and soluble dopamine beta-hydroxylase have identical apparent molecular weights

Dopamine beta-hydroxylase exists as soluble and membrane-bound forms in secretory vesicles. The soluble form of the enzyme contains identical subunits of 72 kDa and the membrane-bound form contains two non-identical subunits of 72 kDa and 75 kDa. The difference in the banding pattern on sodium dodecyl sulfate-polyacrylamide gel electrophoresis suggests the presence of either an extra peptide, or membrane-binding segment, or differential glycosylation of 75-kDa subunits of the membranous form. Soluble and membranous forms of the enzyme were deglycosylated with endoglycosidases to elucidate the contribution of the carbohydrate moieties to the banding pattern on a sodium dodecyl sulfate-polyacrylamide gel. The deglycosylated species of both forms appeared to be identical and showed a decrease in apparent molecular weights to 66 kDa. These results indicate that the banding pattern of soluble and membranous dopamine beta-hydroxylase on sodium dodecyl sulfate-polyacrylamide gel electrophoresis may not be due to a membrane-binding anchor but rather to carbohydrate moieties.