66 A SYMPOSIUM ON RESPIRATORY ENZYMES 



however, with neghgible respiratory activity, demonstrating the 

 possibihty of a reversible oxidative inactivation. 



The inhibition of glycolysis with iodine was subsequently studied 

 more carefully by Gemmill and Hellerman (57). With concentra- 

 tions just high enough to obtain fairly complete inhibition they were 

 able to recover the activity by adding glutathione or cysteine. This 

 suggested strongly that the oxidative inhibition was due to reversible 

 oxidation of enzyme SH-groups. Rapkine (58, 59) then showed that 

 the oxidoreduction between phosphoglyceraldehyde and pyruvic 

 acid was at least one of the partial reactions being blocked by 

 oxidation, presumably of enzyme-SH. This reaction system could be 

 inactivated by S-S-glutathione and reactivated by SH-glutathione. 

 More recently Rapkine found the same reaction reversibly inacti- 



Table 8.— Induced Pasteur eflFect in cell extracts 



vated by dichlorophenolindophenol (personal communication), which 

 might explain my earlier results with the complete glycolytic sys- 

 tem. With these experiments the possibihty of a reversible oxidative 

 inactivation has become firmly established. It is therefore of little 

 significance for the question at issue that, as was shown by Michaelis 

 and Smythe (60), many dyes, irrespective of oxidation-reduction 

 potential, inhibit irreversibly by various mechanisms, or that naphthol- 

 sulfonate indophenol with different yeast preparations leads earlier 

 to irreversible inactivation than in our experience. 



Resides the system studied by Rapkine, a number of partial 

 enzymes of glycolysis were found to undergo oxidative inactivation 

 followed by reactivation with glutathione. These reactions are as 

 follows: 



