St John's University 1 article published in JoVE Biology In Vitro Assay to Measure Phosphatidylethanolamine Methyltransferase Activity Rachel Zufferey1 1 The present report describes an in vitro enzymatic assay to measure phosphatidylethanolamine methyltransferase activity using Leishmania cell extracts. This assay is based on the transfer of a radioactive methyl group from S-[Methyl-3H]adenosyl-L-methionine onto endogenous phosphatidylethanolamine.