434 HERRICK BALTSCHEFFSKY 



The results with vahnomycin (Fig. 3) are given the following tentative 

 explanation (Fig. 4). In R. riibriifri, "the physiological pathway" is con- 

 nected with tzvo phosphorylation sites, one of which is sensitive to vahno- 

 mycin; thus we have the 50",, inhibition. The valinomycin-sensitive site is 

 by-passed when "the PMS-pathway " is used; thus we have no inhibition. 

 In other words, the P/2e^ ratio is assumed to be 2 in "the physiological 

 pathway" and i in "the PMS-pathway". According to this, the rate of 

 electron transport in the latter as compared to that in the former is, 

 obviously, twice as high as would be assumed from a direct comparison of 

 the rates of phosphate esterification. The valinomycin-insensitive phos- 

 phorylation site, which would be common for both pathways, may well be, 

 in some way, closely linked to the primary photochemical reaction, which 

 has been implied in Fig. 4 by connecting this phosphorylation with the 



TABLE I 



Effect of Valinomycin on LIP in Spinach Chloroplasts 



The experimental details were as described in ref. [5]. The final concentrations of 

 the various agents were, where added: 33 x 10 * m ATP, io~* m menadione, 

 I • 3 X 10^* M FMN, io~* M FAD, and 2 x iq-^ m PMS. In the menadione, FMN, 

 FAD and PMS-series, respectively, the values for 100% activity were 58, 28, 57 

 and 53 ?b orthophosphate esterified and the chlorophyll content in each sample 

 o* 12, 0-07, o- 12, 013 mg. respectively. The time for the experiments was 6 min. 



photochemical oxidant. Consequently, there may be two kinds of electron 

 transport-linked phosphorylation in the light-induced formation of ATP 

 in bacterial chromatophores, one being similar to and the other different 

 from electron transport phosphorylation in respiring mitochondria, as is 

 visualized from the data obtained with valinomycin. 



In spinach chloroplasts (Fig. 4) the absence of inhibition by low 

 concentrations ofvalinomycin is tentatively taken to indicate the functioning 

 of only one phosphorylation site, corresponding roughly to the valinomycin- 

 insensitive one in bacteria. The possibility cannot be excluded, that ATP- 

 formation at a site of phosphorylation, similar to the valinomycin-sensitive 

 one in bacteria, has been uncoupled in the spinach chloroplasts during the 

 preparation. 



By measuring the quantum requirement for the formation of ATP we 



