224 METABOLISM AND PHYSIOLOGY 



additional data will be presented concerning this factor, which we 

 propose to call phosphodoxin, e.g., spinach phosphodoxin or Rho do - 

 spirillum nibnim phosphodoxin. 



METHODS 



Experiments on light-induced formation of ATp32 were conducted 

 with a 1 ml reaction mixture containing the following components in 

 /imoles: Tris-HCl buffer, pH 7.8, 48; MgCl2, 2; ADP, 1; Pi + Pi32 

 (containing from 0.5 to 1 //curie), l;bacteriochlorophyllor chlorophyll, 

 less than 30 /igrams. ATp32 -^^s assayed as previously described (8). 

 In some experiments ATP was determined spectrophotometrically 

 with glucose, hexokinase, NADP, and Zwischenferment. The methods 

 used for preparation of chromatophores and chloroplast fragments 

 and for chlorophyll determination were those previously reported (8). A 

 method of isolating the naturally occurring factor has been described 

 elsewhere (8), The reaction mixtures were illuminated laterally in 

 1-cm cuvettes at 2,500 foot-candles. Light intensity was varied by 

 varying the distance of the reaction mixtures from the light source 

 (11). 



RESULTS 



Photosynthetic phosphorylation with R. r^ftrz^w chromatophores was 

 markedly stimulated by the addition of the factor isolated from whole 

 cells of the same organism (Fig. 1). The formation of ATP was more 

 linear with time and fell off slower in the presence of the factor than 

 in its absence. 



One characteristic of the factor (s) is its ability to stimulate photo- 

 synthetic phosphorylation by chromatophores, regardless of the or- 

 ganism from which it is isolated, i.e., an algae, a higher plant, a 

 flagellate, or a bacterium (8). Further demonstration of these cross- 

 reactions between organisms is given in Table 1 and Figs. 2 and 3. 

 The rates of endogenous photosynthetic phosphorylation of both spinach 

 chloroplasts and R. nibrum chromatophores were stimulated by the 

 addition of the factor (s) isolated from spinach, Chroniatiiun, or R. 

 rubnim (Table 1). Photosynthetic phosphorylation by spinach chloro- 

 plasts was strikingly stimulated by the factor isolated from Chroma- 

 tium (Fig. 2), and likewise Chromatium chromatophores were stimu- 

 lated by the factor isolated from spinach (Fig, 3). 



In the presence of the factor, anaerobic conditions did not affect 

 the rates of photosynthetic phosphorylation observed with 72. rubnim 

 chromatophores during a two-minute illumination (Fig. 4, upper two 

 curves). With longer illumination periods, a slight stimulation occurred 



