OXIDATIVE PHOTOPHOSPHORYLATION AND THE 



MEHLER REACTION 



Daviu W. Krog.mann 



Department of Biochemistry, University of Chicago 

 Chicago, Illinois 



Our attention has been directed to the study of photophosphoryla- 

 tion in the presence of indophenol dye (5) . As in the other types 

 of photophosphoryhition, undenatured chloroplasts, light, magnesium 

 ions, inorganic phosphate, and a high-energy phosphate acceptor are 

 necessary. In contrast to the other types of photophosphorylation, 

 when indophenol is used as a cefaclor the phosphorylation reaction 

 is dependent on atmospheric oxygen. Several lines of evidence indi- 

 cate that phosphorylation accompanies the oxidation of reduced in- 

 dophenol rather than its reduction in the Hill reaction. This oxygen- 

 dependent phosphorylation proceeds in the absence of any mano- 

 metrically detectable oxygen consumption or evolution. The re- 

 quirement for oxygen by this system could be rationalized as an up- 

 take of oxygen accompanying phosphorylation masked by an equiva- 

 lent production of oxygen by the Hill reaction. 



Experiments amth Isotopic Oxygen 

 Experiments ^vith isotopically labeled oxygen were undertaken 

 to test this interpretation. It was through the courtesy of Dr. Allan 

 Brown that the mass spectrometer facilities at the Botany Department 

 of the University of Minnesota were made available to us. A de- 

 tailed description of this apparatus and the method of calculation 

 of results have been presented elsewhere (1, 2). In these experi- 

 ments, a phosphorylation reaction mixture was incubated beneath 

 an atmosphere enriched with the mass thirty-four isotope of oxygen. 

 The gas phase above the reaction mixture was continuously moni- 

 tored by the mass spectrometer. The diagram in Fig. I is representa- 

 tive of the results obtained in these experiments. In the initial dark 

 period, there is no change in the concentrations of either the mass 

 thirty-two or mass thirty-four isotoj^es of oxygen. When the light is 

 turned on, there is an immediate and sustained decrease in the con- 



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