CYCLIC AND NONCYCLIC PHOTO PHOSPHORYLATION 181 



TABLE 3 

 Effect of Heat Treatment on Cyclic Photophosphorylation 



ytimoles ATP formed/mg Bchl/hr 

 Additions Heated in air Heated in argon Control 



none 77 201 192 



ascorbate 176 204 203 



phenazine 307 328 307 



methosulfate 



Heat pretreatment was for lOmin at 50°C. The final concentration of ascor- 

 bate was 5 X 10-3 M. The conditions and components of the phosphorylation 

 reaction mixture were the same as given in Table 1. 



at higher concentrations the system became "overreduced" for opti- 

 mum photophosphorylation. The effect of a particular ascorbate con- 

 centration was influenced by the gaseous atmosphere. Thus, an over- 

 reducing effect of a high concentration of ascorbate under anaerobic 

 conditions was mitigated by the admission of air (cf. also 23), 



As shown in Table 4, we have confirmed the effect of ascorbate con- 

 centration in argon and in air on cyclic photophosphorylation. ATP 

 formation in air or argon was strongly inhibited by antimycin A. No 

 appreciable antimycin A- resistant photophosphorylation occurred with 

 the addition of ascorbate alone at any of the ascorbate concentrations 

 tested (10"5 to 10*2 M). 



TABLE 4 



Effect of Ascorbate aiirl Antimycin A on Cyclic 

 Phosphorylation Knder Argon and Air 



Ascorbate 

 concentration 



/imoles of ATP formed/mg Bchl/hr 



Argon Air 



antimycin A antimycin A 



present present 



50 ^g bacteriochlorophyll was used in all cases. Other components of the 

 photophosphorylation reaction mixture were the sameas given in Table 1. Where 

 indicated, 10 ^g of antimycin A was added. 



