Phenylethanolamine N-methyltransferase from the brain and adrenal medulla of the rat: a comparison of their properties.

Two different molecular forms of phenylethanolamine N-methyltransferase (PNMT, EC 2.1.1) have been isolated from the brain and adrenal glands of the rat as indicated by certain of their physicochemical properties, such as: molecular weight estimated on the basis of gel chromatography of Sephadex G-100; pH optima; electrophoretic mobility on acrylamide gel; and steady-state kinetic parameters. The high Km value for the brain PNMT has been assumed to be responsible for the low methylation ratio between norepinephrine and epinephrine in the CNS.