624 LIGHT AND LIFE 



preparation in 40% glycol is usually stable for one week when stored 

 at — 15°C. The glycol permits low-temperature storage without freez- 

 ing. The washed residue is free of myokinase but contains a potent 

 inorganic pyrophosphatase. The preparation does not appear to 

 catalyze the Hill reaction; neither trichloroindophenol, ferricyanide, 

 nor TPN are reduced in light, nor is oxygen evolved. 



Photophosphorylation was observed over a rather wide pH range, 

 from about 6.0 to 8.3, with an optimum at pYL 1.1. This contrasts 

 with the spinach chloroplast system, which shows a sharp optimum 

 at pH 8.0 and almost no activity at pH 7.0 (2) . Generally the dis- 

 appearance of inorganic phosphate was measined, but photophos- 

 phorylation of ADP was also estimated spectrophotometrically by 

 way of glucose 6-phosphate with Zwischenferment-glucose and TPN; 

 glucose-6-phosphate (=:ATP) formation was found to be equivalent 

 to the disappearance of inorganic phosphate. 



Although FMN and menadione each stimulate the chloroplast sys- 

 tem (16), a combination of the two appears to be necessary for the 

 algal system. The synergistic effect between FMN and menadione 

 is shown in Table 2. FMN, however, is not specific for this system; 

 FAD or even riboflavin is also active. Hill reported (15) that with 

 spinach chloroplasts the activity of PMS is due to its photooxidation 

 to pyocyanin. In the Anabaena system, hoAvever, pyocyanin was only 

 10% as active as PMS, and when added together with an equal 

 concentration of PMS, it caused a 40% inhibition. 



As previously described for spinach and R. riibrum (1, 5) , un- 

 couplers of aerobic phosphorylation, such as dinitrophenol or dicu- 

 marol, also inhibit photoj^hosphorylation with the algal system, but 

 again a 10-fold greater concentration is required. Another uncoupler 

 of aerobic phosphorylation, the butyl ester of diiodohydroxybenzoic 

 acid, however, causes 50 9^ inhibition at 1 X 10--' Af, and 100% 



TABLE 2 

 Effect of FMN and Menadione on Photophosphorylation 



•imoIes/3 ml 0.20 0.30 1.0 2.0 



iumoles APi/hr/mg chlorophyll 



FMN 17 36 36 



Menadione 29 



FMN + menadione 72 96 68 22 



The reaction conditions were the same as those in Table 1 , but the PMS was replaced 

 by FMN and menadione, as shown. 



