Question

When O2 is added to an anaerobic suspension of cells consuming glucose at a high rate, the rate of glucose consumption drops significantly as the O2 is consumed; the accumulation of lactate also ceases. First observed by Louis Pasteur in the 1860s, this effect is characteristic of most cells capable of aerobic and anaerobic metabolism.

a) Why does lactate cease to accumulate upon addition of O2?

b) Why does the rate of glucose consumption decrease?

c) What is the mechanistic basis for slowed glucose consumption? (i.e. Which enzymes are being affected and how?

Answer 1

When there is addition of oxygen to an anaerobic suspension of cells it allows converting fermentation to oxidative phosphorylation as a mechanism for reoxidizing NADH and making ATP. As ATP formation is an efficient process in aerobic conditions due to which the amount of glucose required will decrease known as Pasteur effect. This can be easily demonstrated in any tissue or cell suspension that has the capability to perform aerobic and anaerobic glycolysis.

(a) The oxygen allows the anaerobic suspension of cells to converted from lactic acid fermentation to respiratory electron transfer and oxidative phosphorylation as the mechanism for NADH oxidation due to which lactate cease to accumulate.

(b) As the cells produce much more ATP per glucose molecule when they oxidized aerobically, hence they needed less glucose.

(c) As the ATP production increases by aerobic oxidation, the phosphofructokinase-1 is inhibited and slowing the rate of glucose entry into the glycolytic pathway.