622 LIGHT AND LIFE 



grown. Rather stable extracts were prepared by grinding wet cells 

 with 3 volumes ot alumina, followed by extraction with 5 volumes of 

 a solution containing 40% ethylene glycol, 0.1 M Tris buffer pH 8, 

 and 0.01 M ascorbate. All the photophosphorylating activity was 

 present in the 105,000 X g pellet; this contains the chlorophyll and 

 carotenoids, but is essentially free of phycocyanin. The examination 

 by electron microscopy, kindly carried out by A. Shatkin, showed the 

 preparation to consist entirely of smooth vesicles varying in diameter 

 from 30 to 300 m^. These appear to be derived from the peripheral 

 lamellae seen in the electron microgram of intact cells (13) . 



Characteristics of Photophosphorylation in Anabaena Fragments 



As in the particle suspension from R. rubriim described by Frenkel 

 (4) , the Anabaena system catalyzes a substrate-independent, anaerobic 

 photophosphorylation of ADP which requires Mg++ and an added 

 electron carrier. Phenazine methosulfate (Sigma) (PMS) is most 

 effective, although the combination of flavin mononucleotide (FMN) 

 and menadione is also active as an electron carrier. [N.B. The name 

 "phenazine methosulfate" should be considered a trade name. The 

 compound is chemically better defined as methyl phenazonium metho- 

 sulfate, and is derived from the reaction between dimethyl sulfate and 

 phenazine (3) .] 



The experiments were carried out in an illuminated Warburg ap- 

 paratus in which a bank of photoflood bulbs provides more than 

 7000 foot-candles. Such strong illumination is necessary for light 

 saturation. Anaerobic conditions are essential. Attempts to obtain 

 phosphorylation in air, by adding various reducing agents, failed. The 

 aerobic inhibition is largely irreversible, and is probably due to 

 photooxidation. The removal of phycocyanin seems to be responsible 

 for the photooxidation. This interpretation is supported by the fol- 

 lowing observations: particles prepared in 40% dextrin retain the 

 jihycocyanin, and these particles do photophosphorylate in air at 

 about one-half the rate obtained anaerobically. 



Only ADP, and not AMP, acts as a phosphate acceptor. Addition 

 of a glucose-hexokinase trap increases the rate of phosphate utilization. 

 During the early stages ot this study inactive preparations were some- 

 times obtained. Such preparations strongly inhibited photophosphory- 

 lation with spinach chlorojilasts, but this inhibition was overcome 

 by bovine serum albumin (HSA) , which activates these algae prepara- 

 tions for jjhotophosphorylation. This effect of BSA has been de- 

 scribed in oxidative phosphorylation (11). Since it strongly binds a 



