300 DOUGLAS C. PRATT, ALBERT W. FRENKEL, AND DONALD D. HICKMAN 



examined rates of light-induced phosphorylation and have reported rates 

 for preparations from both dark- and light-grown cultures which are a 

 good deal higher than the ones reported here, and in fact appear to be the 

 highest ones reported in the literature for bacterial photo-phosphorylation. 

 Vernon and Ash [9] have reported that light-induced reduction of 

 DPN by extracts from R. riibrum is increased in the presence of magnesium 

 ions. We have also observed a small stimulatory effect of magnesium (or 

 manganese) ions on the photoreduction of DPN. We have noticed, how- 

 ever, that this effect is much more pronounced with cell-free preparations 



TABLE I 



Photochemical Activity of Intact Cells of Rhoduspirillum rubrum and of 

 Chromatophores Derived from Cells Cultured in the Dark and Light 



Initial rates (at light saturation) : 



/xM 



hr. X juM bacteriochlorophyll 

 Preparations from cultures grown in the 



A 



Dark Light 



215 



21-6 



i8-8 



* Corrected for CO 2 production. 



from dark-grown cells (Table I). Repeated washing of the dark-grown 

 preparations almost completely eliminates the photoreducing activity, but 

 such activity can be restored (more or less completely) by the addition of 

 magnesium (or manganese) salts. Repeated washing of preparations 

 obtained from light-grown cells produces a much more gradual loss of 

 activity which can be restored by the addition of magnesium ions. We 

 believe that this behaviour toward magnesium (or manganese) may reflect 

 some subtle differences in the particles derived from light- and dark-grown 

 cells, indicating that either less magnesium (or manganese) is bound by the 

 chlorophyll containing particles from dark-grown cells, or that it is leached 

 out more easily. We hope to obtain more information about this ion effect 

 in the course of work on the development of the bacterial chromatophore. 



