In the rat, the enzyme that methylates norepinephrine to form epinephrine, phenylethanolamine-N-methyl transferase (PNMT), is highly localized in the adrenal medulla. Its activity is controlled by steroid hormones from the adrenal cortex. Frog PNMT differs from the rat enzyme in its pH, ionic strength, and temperature optima, its thermolability, stability in cold, dilute buffer, and rate of migration on starch-block electrophoresis. The substrate specificities of both enzymes are similar, and both are stimulated in vitro by ethylenediamine tetra-acetate (EDTA), and inhibited by tranylcypromine. Unlike the rat enzyme, frog PNMT activity is present in many organs, and does not decline following hypophysectomy. It is suggested that frog PNMT is an uninducible form of the rat enzyme. (Endocrinology 82: 584, 1968)
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Wurtman et al. (1968) studied this question.