246 



F. R. Whatley 



air and under nitrogen were similar at saturating concentrations 

 of PMS, and (iii) there was little effect of CMU on the rate of 

 ATP formation anaerobically with saturating PMS (4). However, 

 some unexpected effects of oxygen on the PMS-catalyzed cyclic 

 photophosphorylation have been found. These effects will be 

 discussed in the context of an interpretation proposed by 

 Tagawa et al. (8) of the effect of oxygen on the cyclic photo- 

 phosphorylation catalyzed by ferredoxin. 



In Table 1 is shown the effect of increasing the concentra- 

 tion of the cof actor, PMS, on the formation of ATP in argon or 



^^^^ The reaction mixture 



Effect of air on cyclic contained, in a final 



photophosphorylation catalyzed by PMS volume of 3 ml, broken 



ATP formed in 15 min. chloroplasts (Pig) 

 (nmoles) containing 0.1 mg 



/^ij- chlorophyll and the 

 ' following in micro- 



^•^ moles: tris buffer, 

 "•^ pH 8.3, 80; MgClg, 10; 

 1.2 ADP, 10; K2HP3204, 10; 

 3.8 and the amounts of 

 8.8 phenazine methosulfate 

 9.2 indicated. The exper- 

 iments were carried 

 out in Warburg manometer vessels at 15° C at 20,000 lux. Prior 

 to turning on the light, the "argon" series was flushed with 

 purified argon gas for 5 minutes. ATP formation was measured 

 as described previously (11). 



in air. Although at the saturating concentration of PMS com- 

 monly employed (3O ^Lgrams per 3 ml reaction mixture) there was 

 no difference between the rate in air or argon, a large stimu- 

 latory effect of air became apparent at lower concentrations of 

 PMS. When 3 jigrams PMS were used the reaction was not satura- 

 ted by PMS (under our experimental conditions), but there was a 

 threefold stimulation by air of the ATP formation. A similar 

 stimulation has also been observed by Jagendorf and Avron (9) . 

 The addition of small amounts of oxygen was found to produce 

 the same effect as air. In Table 2 are reported the results 

 obtained when 3 ngrams PMS were used as the cofactor for cyclic 

 photophosphorylation and small amounts of oxygen gas were added 

 to a reaction vessel of approximately 20 ml capacity. When 10 

 lomoles oxygen had been added the rate of ATP formation was max- 



