CBS and CSE have been reported to re-localise to mitochondria in response to hypoxia, a common feature of the tumour microenvironment, resulting in targeted H2S delivery that can stimulate ATP production and protect mitochondria from oxidative stress.109,153 Accordingly, exposure of SW480 colorectal cancer cells to hypoxia resulted in an enrichment in mitochondria of SQR protein levels and H2S detoxification activity.154 Besides the bioenergetics stimulation, the antioxidant nature of H2S is expected to protect cancer cells from oxidative damage. The gene discussed is CBS; the disease is colorectal cancer.