Glycolysis Pasteur effect

Answer The addition of oxygen to an anaerobic suspension allows cells to convert from fermentation to oxidative phosphorylation as a mechanism for reoxidizing NADH and making ATP. Because ATP synthesis is much more efficient under aerobic conditions, the amount of glucose needed will decrease (the Pasteur effect). This decreased utilization of glucose in the presence of oxygen can be demonstrated in any tissue that is capable of aerobic and anaerobic glycolysis. 

The inhibition of glycolysis by respiration, discovered by Louis Pasteur in studying fermentation by yeast. The consumption of carbohydrate is about sevenfold lower under aerobic conditions than under anaerobic ones. The inhibition of phosphoifuctokinase by citrate and ATP accounts for much of the Pasteur effect. 

Much has been published on the controversial subject of the control of glycolysis. The following brief summary of some of the controls responsible for the Pasteur effect in yeasts is based mainly on a review by Sols and coworkers144 (see also, Fig. 7). (i) Isocitrate dehydrogenase (NAD ) (EC 1.1.1.41), one of the controlling enzymes of the tricarboxylic acid cycle (see Fig. 5), catalyzes the reaction... 

Pasteur Effect The inhibition of glycolysis by oxygen discovered by Pasteur when he found that aerobic yeast cultures metabolize glucose relatively slowly. 

It is a matter of common observation that most metabolic sequences operate most of the time at considerably less than maximal rate. This generalization is especially evident in higher animals—the respiratory rate of muscle at rest, for example, is a small fraction of the rate of working muscle—but it is valid for other types of organisms as well. The observation that glycolysis in yeast proceeds at less than the maximal rate in the presence of air (the Pasteur effect) attracted much interest for years. 

Phosphofructokinase (EC 2.7.1.30) catalyses the phosphorylation of fructose-6-phosphate to fructose-1,6-biphosphate as the key regulatory enzyme of glycolysis. Inhibition of phosphofructokinase by adenosine triphosphate and its activation by adenosine monophosphate and inorganic phosphate is held responsible for the induction of the Pasteur effect (for review see Ramaiah 1974). 

Because only two molecules of ATP are produced per glucose metabolized under anaerobic conditions, the cell must utilize additional glucose at a faster rate in order to maintain the pool of intracellular ATP. This step is accomplished through activation of the enzyme phosphofructokinase (Fig. 1.10), which, in turn, increases carbon flow through glycolysis. The increase in rate of glucose breakdown under anaerobic conditions is known as the Pasteur effect. This phenomenon is only observable when glucose concentrations are low, approximately 0.9 g/L (Walker, 1998). 

The early work of Meyerhof showed that there was an intimate connection between resynthesis of carbohydrate and aerobic metabolism. When the production of lactic acid by tissues under anaerobic conditions was compared with the production of lactic acid under aerobic conditions, it was found that the uptake of 1 mole of respired oxygen inhibited the formation of 1 to 2 moles of lactic acid i.e., three to six times as much lactic acid as could have been oxidized by the observed oxygen uptake. This phenomenon of the suppression of glycolysis under aerobiosis has been called by Warburg the Pasteur effect. 

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