548 



LIGHT AND LIFE 





8 



7 



TPN 



oxygen 

 n-__o -O O 



I 1 L I 



8 



to 

 5 ^ 



hi 



>^ 



=^ 



10 15 20 



20 O 5 

 minutes 

 Fig. 22. Photophosphorylation and oxygen evolution by isolated chloroplasts in 

 the presence and absence of FMN (Arnon, Whatley, and Allen, 18, 18a). ^A, 

 microatoms. 



evolution. It is assumed that the intact cell has suitable regulatory 

 mechanisms for keeping cyclic and non-cyclic photophosphorylation 

 in balance. 



The marked increase in phosphorylation accompanied by a total 

 abolition of oxygen evolution and TPNHo accimiulation, shown in 

 Figs. 22 and 23, occurred on adding 0.1 micromoles of FMN or 0.2 

 micromoles of vitamin K (in a final volume of 3 ml) . However, the 

 addition of even extremely minute amounts of either FMN or vitamin 

 K had a measurable effect on reaction 4. Table 13 shows that the 

 addition of as little as 0.0002 to 0.0005 micromoles of FMN or vitamin 

 K increased ATP formation without appreciably depressing oxygen 

 evolution (and the corresponding TPNH^ accumulation) . Similar 

 effects were observed on adding small amounts of phenazine methosul- 

 fate (Table 14) . 



As will be discussed more fully later, the addition of small amounts 

 of one of these catalysts of photosynthetic phosphorylation had an in- 

 fluence on carbon assimilation. Concentrations of FMN and vitamin 

 K which suppressed oxygen evolution (and TPNH^ accumulation) 

 also suppressed reductive CO2 fixation, but the minute concentrations 



