346 DANIEL I. ARNON 



These findings are in agreement with the recent resuhs of Wessels [54], 

 Jagendorf and Avron [55] and Nakamoto, Krogmann, and Vennesland 

 [56], that photosynthetic phosphorylation with suboptimal amounts of 

 cofactors is oxygen-dependent but becomes oxygen-independent at higher 

 concentrations of cofactors. 



In charting their subsequent investigations Arnon and his associates 

 laid special stress on the anaerobic photosynthetic phosphorylation which 

 proceeds in isolated chloroplasts at optimal catalytic concentrations of 

 FMN and vitamin K. They considered this type more fundamental to 

 photosynthesis in general than the oxygen-catalyzed type because it would 

 also apply to bacterial photosynthesis, in which oxygen cannot be involved. 



INTENSE LIOIT ond HIGH CHLOROPHYLL 



0-003 001 0-OS 0-1 0-3 10 

 //moles vit. K3 added 



0-003 001 0-OS 0-1 0-3 10 

 //moles FMN added 



Fig. 3. Effect of vitamin K3 (2-methyl-i,4-naphthoquinone) and FMN con- 

 centration on cyclic photophosphorylation by spinach chloroplasts in nitrogen and 

 air at high light intensity. The reaction mixture (3 ml. final volume) included 

 chloroplast fragments (Cij) containing i ■ 5 mg. chlorophyll ; and in micromoles : 

 tris buffer pH 8 • 3, 80 ; K2H32PO4, 20 ; ADP, 20 ; MgS04, 5 ; and TPN, o • 3 (only 

 in the FMN series). FMN and vitamin K3 were added as indicated. The reaction 

 was run for 5 min. at an illumination of 50 000 Lux (Tsujimoto, Hall, and Arnon 

 [92]; Arnon, Whatley, and Allen, unpublished data, 1954). 



Soon after the discovery of photosynthetic phosphorylation in isolated 

 chloroplasts, Frenkel [57] reported a similar phenomenon in the photo- 

 synthetic bacterium Rhodospirilhnn ruhrum. Although Frenkel suggested 

 that the light-induced ATP formation in bacterial preparations was 

 similar to that in chloroplasts, the similarity seemed uncertain at first, 

 because Frenkel's photophosphorylation system, which was a sonic 

 macerate of R. rubrum cells, differed in several respects from its counter- 

 part in isolated chloroplasts [13]. Frenkel's preparations became substrate- 

 dependent after washing; the rate of phosphorylation was doubled on 

 adding a-ketoglutarate [57]. But in later experiments he ruled out the 

 dependence on an added chemical substrate [58] and the equivalence of 

 chloroplast and bacterial photophosphorylation seemed probable. 



