Different forms of adrenal phenylethanolamine N-methyltransferase: species-specific posttranslational modification.

Phenylethanolamine N-methyltransferase was purified from rat and cow adrenal glands. The enzymes from the two species have the same molecular weight of 31,000, but differ in electrophoretic mobility. During polyacrylamide gel electrophoresis, the rat form migrates faster than the bovine form. Antibodies to bovine enzyme precipitated equally well the rat and cow form of the enzyme, but antibodies against rat enzyme precipitated poorly the bovine form. In contrast, both antibodies recognized a similar protein in the in vitro translation products of poly(A+)mRNA isolated from cow adrenal glands. The results suggest that the primary protein structure of rat and bovine enzyme is similar and that differences in electrophoretic mobility are due to posttranslational modification of the enzyme molecule.