Abstract

Phenylethanolamine N-methyltransferase (EC 2.1.1) was purified from the supernatant and particulate fractions of bovine adrenal medulla. The bulk of the enzymatic activity was associated with the supernatant fraction, but 15-20% of the activity was found to be associated with the particulate fraction (100,000 x g sediment). The enzyme from the particulate fraction was solubilized and partially purified. The enzyme from the supernatant fraction was isolated in pure form and has a molecular weight of approximately 40,000. The enzyme also occurs in two higher molecular forms, with molecular weights of approximately 80,000 and 160,000. Differently charged isozymes were separated from the low molecular weight form of the enzyme by DEAE-Sephadex chromatography and polyacrylamide disc gel electrophoresis. Amino acid analysis revealed a relatively high content of dicarboxylic acids or their amides and the presence of hexosamine. It is possible that the charge isozymes may arise by deamidation, or that a difference in the carbohydrate residues exists. The two major charge isozymes (designated here as B₁ and B₂) are indistinguishable from each other on immunoelectrophoresis. The immunochemical analyses revealed heterogeneity of adrenal phenylethanolamine N-methyltransferase among different species. It appears that the corticoid-inducible, mammalian adrenal enzyme is immunologically distinguishable from the uninducible, frog adrenal enzyme.