Becker's World of the Cell 9th Edition by Lewis Kleinsmith, Jeff Hardin, Gregory Paul Bertoni

Exercise 12

Life without phosphofructokinase. Many bacteria do not have phosphofructokinase-1 (Gly-3)and thus cannot convert glucose to fructose-1,6-bisphosphate. Instead they use a pathway known as the Entner-Doudoroff pathway to partially oxidize glucose and convert it to two three-carbon molecules. See if you can draw the products of the first three steps of the pathway based on the following description:
(a)In the first step, the ring form of glucose-6-phosphate is oxidized at carbon 1 to form 6-phosphogluconolactone, as the coenzyme NADP+ is reduced to NADPH + H +.
(b)Next, the ring is broken by hydrolysis to form the carboxylic acid 6-phosphogluconate, which resembles glucose-6-phosphate but is more oxidized at carbon 1.
(c)After a molecule of water is removed, a molecule of 2-keto-3-deoxy-6-phosphogluconate is formed.
(d)Because an aldolase splits this six-carbon molecule into pyruvate plus glyceraldehyde-3-phosphate (which is then converted to another molecule of pyruvate), how will the final ATP yield per glucose compare with typical glycolysis
(e)Given an alternate source of cellular ATP, how would you predict lactic acid production might be affected by the addition of arsenate (see Problem)in these bacteria compared to bacteria performing standard glycolysis
Problem
Arsenate Poisoning. Arsenate (HAsO 4 2 )is a potent poison to almost all living systems. Among other effects, arsenate is known to uncouple the phosphorylation event from the oxidation of glyceraldehyde-3-phosphate. This uncoupling occurs because the enzyme involved, glyceraldehyde- 3-phosphate dehydrogenase, can utilize arsenate instead of inorganic phosphate, forming glycerate-l-arseno-3-phosphate. This product is a highly unstable compound that immediately undergoes nonenzymatic hydrolysis into glycerate-3-phosphate and free arsenate.
(a)In what sense might arsenate be called an uncoupler of substrate-level phosphorylation
(b)Why is arsenate such a toxic substance for an organism that depends critically on glycolysis to meet its energy needs
(c)Can you think of other reactions that are likely to be uncoupled by arsenate in the same way as the glyceraldehyde-3-phosphate dehydrogenase reaction