180 METABOLISM AND PHYSIOLOGY 



Effect of aging and heat treatments 



As previously reported (see Table 1 in ref. 5), chromatophores 

 from R. rubynm, when freshly prepared under anaerobic conditions, 

 have a complete system for cyclic photophosphorylation. Cyclic 

 photophosphorylation in chromatophores (unlike chloroplasts) proceeds 

 without the addition of exogenous cof actors or water-soluble extracts. 

 When chromatophores were prepared under argon (22), even washing 

 them three times in succession had little effect on phosphorylating 

 activity (cf. 26). 



The full phosphorylating activity of chromatophores stored anaero- 

 bically (under argon) at ca. 4 °C was readily restored to original levels. 

 As shown in Table 2, full phosphorylating activity was restored to 

 chromatophores stored for 30 days by the addition of ascorbate, 

 DPNH2 or phenazine methosulfate. In both fresh and aged chromato- 

 phores, phosphorylation, in the presence of ascorbate or DPNH2 but 

 in the absence of phenazine methosulfate, was completely inhibited 

 by antimycin A. 



Table 3 shows that chromatophores heated in air for 10 min, at 

 50 °C lost about 60 per cent of their endogenous phosphorylating activ- 

 ity. This loss of activity was restored by the addition of phenazine 

 methosulfate or ascorbate. Heating at 50 °C under argon caused no 

 impairment of phosphorylating activity. 



It appears that the loss of phosphorylating activity on aging or 

 heating in air is probably the result of the oxidation of one or more 

 electron carriers. Either this oxidation is reversed by the addition of 

 a reductant (ascorbate or DPNH2), or the oxidized site may be by- 

 passed by the addition of phenazine methosulfate. 



Effect of redox agents 



Horio and Kamen (26) have shown that a high phosphorylation 

 activity of chromatophores depended on the presence of an appropriate 

 amount of ascorbate to provide a redox potential of about volt. At 

 lower concentrations of ascorbate the system was "overoxidized" and 



TABLE 2 

 Restoration of Cyclic Photopliosphorylatioii in Aged Clironiatophores 



/imoles ATP/formed/mg Bchl/hr 

 Additions fresh aged 



Illumination and components of the phosphorylation reaction mixture were 

 the same as given in Table 1. 



