Arsenate is a toxic ion that can interfere with both glycolysis and oxidative phosphorylation. Arsenate resembles inorganic phosphate (P) and can replace it in many enzymatic reactions. One such reaction is catalysed by glyceraldehyde 3-phosphate dehydrogenase in glycolysis. Arsenate competes with phosphate for entry into the active site of glyceraldehyde 3-phosphate dehydrogenase and upon completion of the reaction, instead of the normal product, 1,3-bisphosphoglycerate, the mixed anhydride 1-arsenato- 3-phosphoglycerate is formed: this undergoes rapid spontaneous hydrolysis into arsenate plus 3-phosphoglycerate, the latter being a normal intermediate in glycolysis, so glycolysis is able to proceed from the step at 3-phosphoglycerate. What would be the effect of arsenate in glycolysis? (a) Arsenate activates glycolysis so that more ATP and NADH is generated for every glucose molecule. In the presence of arsenate there is no net formation of ATP from glycolysis, but NADH generation is not directly affected Arsenate brings glycolysis to an abrupt stop with immediate lethal consequences In the presence of arsenate glycolysis produces fewer ATP and NADH molecules per glucose molecule. Arsenate does not affect the number of ATP or NADH molecules generated per glucose molecule. (b) (c) (d) (e)
