433 



Birgit Vennesland 



(12) 

 set up . The contents of one of the vessels were analyzed for phosphate 



at the point where the manometrlc changes showed that ATP had reached a 



maximum (ATP-ase can also be followed with this procedure). At the same 



time, more FMN was added from the side-arm of the other vessel, to show 



how the phosphorylation was reactivated by this reagent. Examination of the 



flavin fluorescence at the first inhibition point revealed that the flavin was 



almost completely reduced, and that it remained reduced even when the 



light was turned off. 



The important discovery of chloroplast photophosphory lotion by Arnon ap- 

 pears to have lent great complexity to the Hill reaction. In connection 

 with the complexity, I have a bad conscience, and I should like to make a- 

 mends here. After Arnon hod distinguished between stoichiometric and 

 cyclic photophosphorylation, we suggested that one might differentiate a 

 third kind, which we called oxidative photophosphorylation. Krogmann had 

 made a study of indophenol supported photophosphorylation in my laboratory, 

 and we were struck by the O^ requirement for photophosphorylation sup- 

 ported by indophenol dyes. This was at a time when there was a great em- 

 phasis on anaerobic cycles with other cofactors for photophosphorylation, 

 and I thought that the indophenol system must be different. I am convinced 

 now that the apparent greater requirement of the indophenol system for O^ 

 under some conditions is due to the fact that this reagent is less readily oxi- 

 dized than a reagent like flavin. 



I would therefore like to withdraw the suggestion that we differentiate 

 oxidative photophosphorylation from non-oxidative. I am not repudiating 

 data, but the judgment about selecting a new name. One shouldn't com- 

 plicate terminology beyond necessity. At the present time I think that all 

 photophosphorylation is oxidative, in the sense that it occurs when a suitable 

 reductant, formed in the light, is oxidized by the oxidized form of a Hill re- 

 agent. Seeri inthis light, photophosphorylation is a "substrate" phosphoryl- 

 ation' ' ' . It appears to me that most of the phenomena studied in con- 

 nection with photophosphorylation are compatible with this view, and that 

 none disprove it. 



I believe further that the catalytic cofactors function by a process which 

 involves evolution and reconsumption of oxygen. Either of these two reac- 

 tions may be rate-limiting for the cycle. It is consequently to be expected 

 that an inhibitor of the oxygen-evolving step might be less effective under 

 "anaerobic" than under "aerobic" conditions. This may not be the only 



