CYCLIC ANDNONCYCLIC PHOTO PHOSPHORYLATION 179 



argon. The ATP or the glucose-6-phosphate formed was determined 

 by the magnesium ammonium phosphate precipitation method (24) or by 

 the siliconized celite column method (25). Crystalline lactate dehydro- 

 genase (from muscle), crystalline alcohol dehydrogenase, antimycin 

 A, and hexokinase (Type III) were purchased from Sigma Chemical 

 Co. Hydrogenase was partially purified from Desulfo vibrio desulfuri- 

 cans on a DEAE-cellulose column. 



RESULTS 



I. CYCLIC PHOTOPHOSPHORYLATION 



Inactivation by pretreatment with salt at pH 5.0 



Acidification to pH 5, with acetate buffer, resulted in a coagulation 

 of chromatophores without impairment of phosphorylating activity. 

 However, when the acidification was accompanied by the addition of 

 salt, an appreciable loss of phosphorylation occurred. As shown in 

 Table 1, the loss of phosphorylation is due to the high ionic strength at 

 pH 5, and not to the kind of salt. Ionic strength lower than 0,2 at pH 5 

 or high ionic strength at pH 7.8 had little effect. The inhibitory effect 

 of high salt concentration at pH 5 was observed in the endogenous sys- 

 tem as well as in the presence of phenazine methosulfate (Table 1). 

 Attempts to reactivate phosphorylation in the salt-treated chromato- 

 phores were unsuccessful. 



TABLE 1 

 Inactivation of cyclic photopliosphorylatioii by pretreatinoit ivith salt 



//moles ATP formed/mg 

 Pretreatment . ■ . ,.u u Bchl/hr 



with salt lomc strength pH endogenous PMS 



Prior to thephotophosphorylation reaction the chromatophores were exposed 

 for 5 minat 0°C to the indicated salt mixture, collected by centrifugation (5 min) 

 and resuspended in 0.1 M tris buffer, pH 7.8. The reaction mixture for photo- 

 phosphorylation included in a final volume of 3 ml, chromatophores (containing 

 100 yt/g bacteriochlorophyll), 1 mg hexokinase and the following in //moles: tris 

 buffer, pH 7.8, 100; MgCl2, 5; ADP, 0.5; K2HP32O4, 10; D-glucose, 30; and 

 where indicated, phenazine methosulfate (PMS), 0.3. The reaction was run at 

 20°C for 15 min in the light (20,000 lux). 



