Decreased glycolysis, increased reductive glutamine metabolism and glutamine-fueled oxidative phosphorylation in cancer cells cultured at pH 6.5 compared to pH 7.4.In vivo, glutaminase inhibitor BPTES significantly reduced growth of tumors comprised of cells pre-adapted to pH 6.5 compared to tumors from cells pre-adapted to pH 7.4. The gene discussed is GLS; the disease is cancer.