146 CONTROL MECHANISMS IN CELLULAR PROCESSES 



whether there is more than one cause for a Pasteur effect or whether 

 there is unity in Pasteur effects. It has been assumed that most of 

 the pubhshed data are correct and that they have been interpreted 

 with the knowledge at the time at which the work was carried out. 

 The assumption then that there is unity in the biological world has 

 as unavoidable corollary that some of the investigators created arti- 

 facts mimicking nature but not imitating it. There is great danger 

 in making such decisions; nevertheless, it will be considered in the 

 following paragraphs that there is one Pasteur reaction only. 



In spite of the great progress made in our knowledge of inter- 

 mediary metabolism, there are now, as there were in 1939 (Burk, 

 1939 ) , still three great groups of Pasteur reaction explanations : ( a ) 

 a direct oxygen inactivation of the glvcolvtic process; (b) the ac- 

 cumulation of an inhibitor of the glycolytic process due to aerobic 

 conditions, and ( c ) competition of oxidative and glycolytic processes 

 for a common intermediate. Only the most recent investigations 

 will be dealt with in anv detail. 



Direct Oxygen Inactivation. Lipmann (1942) reviewed the ex- 

 perimental observations on oxygen inhibition of glvcolvsis. Special 

 attention was given to the action of redox dyes. At that time Lip- 

 mann concluded that the most likely site of action was inhibition of 

 triose phosphate dehvdrogenase. Recently the inhibitory effect of 

 methylene blue on aerobic glycolysis was reinvestigated (Glogner 

 et al., 1960), and the conclusion was reached that the aerobic inhibi- 

 tion of glycolysis was due to peroxide formation and a consequent 

 decrease in DPN content of the cells. 



It is not necessarv, however, to inactivate enzymes or cofactors 

 with redox dyes. In experiments on pea-seed extracts. Hatch and 

 Turner (1959) pinpointed an aerobic inhibition of triose phosphate 

 dehydrogenase. This reaction was reversible (as a Pasteur reaction 

 should be ) . Later investigations showed that pea-seed extracts have 

 indeed a mechanism by which protein-bound SH groups can be 

 reversibly oxidized and reduced through pyridine nucleotide depend- 

 ent enzymes (Hatch and Turner, 1960). The actual inactivation 

 of triose phosphate dehydrogenase was presumably non-enzymatic. 

 However, if this observation can be generalized for in vivo condi- 

 tions, this non-enzymatic inactivation should be cyanide sensitive, 

 since cyanide mimicks an anaerobic condition even in the presence 

 of oxygen ( cf . Lynen, 1957 ) . 



