The reversible conversion of leukotriene C4 (LTC4) to leukotriene D4 (LTD4) is catalysed by gamma-glutamyl transferases 1 (GGT1) and 5 (GGT5). GGTs are present on the outer surface of plasma membranes and are a heterodimer of a heavy and a light chain. Its action involves the hydrolysis of the gamma-glutamyl peptide bond of glutathione and glutathione conjugates, releasing glutamate. In this example, LTC4 is a glutathione conjugate that is hydrolysed to LTD4 (Anderson et al. 1982, Wickham et al. 2011).