Purification and partial characterization of histamine N-methyltransferase from bovine brain

S-Adenosylmethionine:histamine N-methyltransferase (EC 2.1.1.8.) (HMT) catalyzes the transfer of a methyl group from S-adenosyl-l-methionine to histamine resulting in the formation of tele-methylhistamine and S-adenosyl-l-homocysteine. In the present study, we purified HMT from bovine brain since this enzyme has been suggested to have some different kinetic properties from that from mouse or rat brain. The overall purification was about 8000-fold with a 2.9% yield. The specific activity of the final preparation was 517 nmol/min/mg protein. The pivotal steps in the purification consisted of ammonium sulfate precipitation, linear gradient DEAE-cellulose chromatography and elution with histamine and S-adenosylmethionine in DEAE cellulose chromatography. Bovine brain HMT could not be retained on the affinity columns using S-adenosylhomocysteine and histamine as ligands under the conditions tested. Molecular weight of the purified enzyme was determined to be 33,200 dalton by SDS-polyacrylamide gel electrophoresis. A pI value of 5.9 was obtained by isoelectric focusing. Amodiaquine and metoprine competitively inhibited the enzyme activity with respect to histamine with K_i values of 7.5 and 58 nM, respectively.