The function of LTC4S (leukotriene C4 synthase, Ensembl gene identifier ENSG00000213316) is as follows. Catalyzes the conjugation of leukotriene A4 with reduced glutathione (GSH) to form leukotriene C4 with high specificity (PubMed:23409838, PubMed:27365393, PubMed:27791009, PubMed:7937884, PubMed:9153254). Can also catalyze the transfer of a glutathionyl group from glutathione (GSH) to 13(S),14(S)-epoxy-docosahexaenoic acid to form maresin conjugate in tissue regeneration 1 (MCTR1), a bioactive lipid mediator that possess potent anti-inflammatory and proresolving actions (PubMed:27791009). {ECO:0000269|PubMed:23409838, ECO:0000269|PubMed:27365393, ECO:0000269|PubMed:27791009, ECO:0000269|PubMed:7937884, ECO:0000269|PubMed:9153254}.