LIGHT-INDUCED PHOSPHORYLATION 433 



to this problem, namely, inhibitor studies, measurements of the quantum 

 requirement of light-induced ATP-formation, and work with pre-aged 

 preparations. It may be pointed out, that all these experiments, except 

 for some inhibitor studies, have been done with bacterial chromatophores, 

 where the above-mentioned possibility of working with two different 

 pathways for the electron transport has been utilized. 



Recently, McMurray and Begg [13] reported that an antibiotic named 

 valinomycin completely uncoupled the oxidative phosphorylation in 

 animal mitochondria. The effect of this agent upon light-induced phos- 

 phorylation in bacteria and in plants was tested [7, 14]. 



^ 60 



^ 40 



20 



I 2 3 6 



/yM valinomycin 



Fig. 3. Effect of valinomycin on LIP in R. rubrnvi. The experimental details 

 were as described in ref. [3]. The final concentrations of the various agents were, 

 where added : 3 3 x io~-' m ATP, and 3 -3 x io~* M PMS. = the series without 

 PMS; • = the series with PMS. Without PMS, 100% activity = 34- 5 «b ortho- 

 phosphate esterified in 20 min. With PMS, ioo"o activity = 40- 5% orthophos- 

 phate esterified in 6 min. In all samples the "OD^oo " was 0-28. 



In chromatophores oi R. nibrmii (Fig. 3) less than micromolar concen- 

 trations of the antibiotic gave a partial inhibition when "the physiological 

 pathway" for electron transport was used. Titration to much higher con- 

 centrations of inhibitor showed a levelling off at about 50"o inhibition. On 

 the other hand, phosphorylation in " the PMS-pathway" was not significantly 

 inhibited. Such an absence of effect with low concentrations of inhibitor 

 was encountered also in the experiments with spinach chloroplasts, as is 

 demonstrated in Table I. Irrespective of whether menadione (vitamin K3), 

 FININ, FAD, or PMS was used as added electron carrier, no marked 

 inhibition was seen wdth the low concentrations of valinomycin. 



VOL n. 2F 



