Properties of norepinephrine N-methyltransferase from pigeon brain

Epinephrine concentration in pigeon hypothalamus was higher on an absolute basis and as a percentage of total catecholamine concentration that in other regions of pigeon brain or in rat hypothalamus. Norepinephrine N-methyltransferase (NMT; the epinephrine-forming enzyme) from pigeon brain had Km values for S-adenosyl-L-methionine and L-norepinephrine of 24 +/- 1 and 101 +/- 4 micrometer, respectively. The enzyme was inhibited by excess L-norepinephrine and by several arylakylamines that earlier had been identified as NMT inhibitors with the enzyme from mammalian brain and adrenal medulla. These results indicate that pigeon brain NMT is similar to that in mammalian brain and adrenal glands and can be inhibited by agents previously used to deplete brain epinephrine selectively in rats. The use of pigeons as experimental subjects in studies on the possible role of epinephrine-forming neurons in behavior is suggested.