N-acetyl serotonin methyl transferase (ASMT) is the last enzyme in the melatonin synthesis pathway Evidence linking autism-related disorders with disorders of melatonin metabolism and more specifically with mutations of the gene encoding ASMT prompted us to investigate the properties and localization of this enzyme As a first step we undertook to overproduce the protein in a recombinant host Early attempts to produce ASMT in recombinant Escherichia con yielded only insoluble and heavily degraded material However recombinant ASMT (rASMT) could be produced in soluble active form and purified in milligram amounts when the gene was cloned and expressed in Leishmania tarentolae (C) 2010 Elsevier Inc All rights reserved