ENZYMATIC N‐METHYLATION OF INDOLEAMINES BY MAMMALIAN BRAIN: FACT OR ARTEFACT?

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Abstract
Abstract— Indoleamine‐N‐methyltransferase (INMT) activity in brain and other tissues from various species was investigated. Using conventional radiochemical assay techniques it was found that apparent INMT activity in brain was linear with time and concentration of protein, indoleamine substrate and methyl donor (S‐adenosylmethionine). However, examination of the reaction products by means of exhaustive thin‐layer chromatographic analysis failed to reveal evidence of significant N‐methylation of tryptamine or N‐methyltryptamine by S‐adenosylmethionine. By contrast, with other tissues, notably rabbit lung. N‐methylation of indoleamine was reproducibly demonstrable. The significance of these findings with reference to the transmethylation hypothesis of schizophrenia is discussed.