COX4I1 and glioma: Metabolites involved in this process, including cysteine (2-fold), methionine (1.5-fold), and GSH (10-fold), were upregulated in the COX4-1-overexpressing glioma cells (Figure 5), suggesting that the transsulfuration pathway is more active in cells expressing the COX4-1 isoform than in cells expressing COX4-2.