A simplification of the enzymatic isotopic assay for serotonin is described, Serotonin is converted to [3H]melatonin by a two-step reaction: N-acetylation of serotonin using acetic anhydride, followed by O-methylation with the enzyme hydroxyindole O-methyltransferase (EC 2.1,1.4) and S-adenosyl-l-[methyl-3H]methionine as methyl donor. The present assay avoids the use of unstable acetylating enzyme, rat liver N-acetyltransferase (EC2.3,1.5). Blank values are lowered considerably and the sensitivity is doubly increased. Two-tenths micromole of serotonin per 30 μl of sample in tissue homogenates can be measured. © 1978.
Hammel, I., Naot, Y., Ben-David, E., & Ginsburg, H. (1978). A simplified microassay for serotonin: Modification of the enzymatic isotopic assay. Analytical Biochemistry, 90(2), 840–843. https://doi.org/10.1016/0003-2697(78)90179-3