Arylamine N-methyltransferase. Methylation of the indole ring.

Arylamine N-methyltransferase catalyzes the novel methylation of the ring nitrogen of tryptamine and pyrrole as well as a number of other arylamines including aniline and its derivatives. S-Adenosyl-L-methionine serves as donor. Tyramine, indole, benzylamine, and desmethylimipramine were inactive as methyl group acceptors. The enzyme was purified from rabbit liver to electrophoretic homogeneity and was characterized as a protein monomer of 27,000 daltons with a pI of 4.8. The kinetic mechanism appears to be rapid equilibrium random Bi-Bi.