In molecular biology the MAPEG family of proteins are a group of membrane associated proteins with highly divergent functions. Included are the 5-lipoxygenase-activating protein, leukotriene C4 synthase, which catalyzes the production of leukotriene C4 (LTC4) from leukotriene A4 (LTA4), and microsomal glutathione S-transferase II (GST-II), which also produces LTC4 from LTA4.