Glyceraldehyde 3 phosphate dehydrogenase (GAPDH) is well known as one of the key enzymes involved in glycolysis. GAPDH is constitutively expressed in almost all tissues at high levels, therefore antibodies against GAPDH are useful as loading controls for Western Blotting. Some physiological factors, such as hypoxia and diabetes, increase GAPDH expression in certain cell types.