Chapter 9, Problem 9.12PS

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:

1. (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⁺.
2. (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.
3. (c) After a molecule of water is removed, a molecule of 2-keto-3-deoxy-6-phosphogluconate is formed.
4. (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?
5. (e) Given an alternate source of cellular ATP, how would you predict lactate production might be affected by the addition of arsenate (see Problem 9-11) in these bacteria compared to bacteria performing standard glycolysis?