4. The lactate shuttle hypothesis is that when ATP demand is high in a cell, glycolysis proceeds rapidly, producing pyruvate faster
than it can be converted to acetyl CoA. The excess pyruvate is converted to lactate, which is then shuttled to tissues that oxidize it (by first converting it back to pyruvate, which feeds the Krebs cycle and Ox Phos.)
a. In a cell that is performing glycolysis rapidly, the comversion of pyruvate to lactate is catalyzed by the enzyme lactate dehydrogenase
pyruvate + NADH + H+ à lactate + NAD+
Write the reaction that must occur in a cell that hosts oxidation of lactate, assuming that LDH is also the catalyst there. Under what
cellular conditions might the reaction be favorable in either type of cell?
Lactate + NAD+à pyruvate + NADH + H+
In the lactate producing cell, high [NADH] and [H+] would be favorable. In the lactate receiving cell, high [NAD+] would be favorable.