Properties of norepinephrine N-methyltransferase from rat, cat and chicken brain

Abstract

1. Kinetic properties of norepinephrine N-methyltransferase (NMT) in ammonium sulfate fractions from rat, cat and chicken brain were studied. 2. For all three enzymes, K m values for S-adenosyl-methionine—the methyl-donating substrate—were lower than those for l-norepinephrine—the methyl-accepting substrate. For both substrates, K m values were lowest for cat, intermediate for rat, and highest for chicken brain NMT. 3. The enzymes from all three species were inhibited by excess concentrations of l-norepinephrine. 4. The enzymes were inhibited by various ring-substituted benzylamines and α-methylbenzylamines, and the structure-activity relationships and stereospecificity of this inhibition were similar for the enzymes from all three species. 5. Though quantitative differences exist, NMT from rat, cat and chicken brain seems to be qualitatively similar both in substrate kinetics and susceptibility to inhibitors.