Multiple forms of rabbit lung indoleamine-N-methyltransferase.

1. Two molecular forms of rabbit lung indoleamine-N-methyltransferase have been isolated by hydroxylapatite chromatography. The results of molecular weight determination by gel nitration and of isoelectric focusing suggest that the two enzymatic forms differ in the electrical charge. 2. Both enzymatic forms exhibit similar kinetic parameters toward S-adenosylmethionine and toward inhibitors competitive with S-adenosylmethionine. The Km values of the two molecular forms toward N-methyltryptamine are similar to the one obtained with enzyme mixture, while the Km values of both forms toward tryptamine are lower than the one found with enzyme mixture. 3. The possibility of a specific regulation of psychotomimetic N,N-dimethylindoleamines production is suggested.