Glycolysis: isoenzyme equipment

When Otto Warburg discovered that tumor cells produce high levels of lactate even in the presence of oxygen around 1920 he thought that a defect in mitochondrial respiration would be the cause of the so called aerobic glycolysis. Such a defect could never been demonstrated.
Today it is generally accepted that a shift in the isoenzyme equipment of distinct glycolytic enzymes is the main cause of the increased aerobic glycolysis in tumor cells.