Cell lysates and mitochondria from human cancer lines derived from cervix (HeLa), colon (Colo741) adenocarcinomas, liver (HepG2) carcinoma and from human skin fibroblasts and human embryonic kidney (HEK293) cells were studied to evaluate the content of both the inhibitor IF1 and the β subunit of ATP synthase, Fig. 1A, B. This evidence concerns the gene ATP5IF1 and cancer.