PHOTOSYNTHliTIC IM losPl lORYLATION I 09 



tion of lipoic acid is unlikely (12). Chelating agents, such as o-phenanthroline or 

 8-hydroxyquinoline, are only effective at rather high concentrations (12, 20). 



An interesting finding is that phenazine methosulfate, or ascorhate, when pres- 

 ent with an excess of reducing agent, or in the presence of each other, tail to ac- 

 tivate photophosphorylation, and in fact become inhibitory { 2). Likewise, a 

 catalytic amount of 2,6-dichlorophenolindophenol, ordinarily an activator, pro- 

 foundly diminishes the activating effect of phenazine methosulfate (20). 



IMMUNOCHEMICAL STUDIES 



Recently, Newton and Levinc (22) have begun a series of researches based on 

 an immunochemical approach. They have shown that antisera directed specifically 

 against different immunologically active sites in the chromatophores, chromato- 

 phore fragments, cell walls of Chromatium, and intracellular proteins can be ob- 

 tained in the usual manner by injection of suspensions of these cellular derivatives, 

 or of whole cells, into rabbits. Cross-reactions between antisera directed against 

 the chromatophore fragments and a number of cellular macromolecules, including 

 wall polysaccharide, intracellular lipoprotein and polysaccharide from chromato- 

 phore fragments, have been studied, using such procedures as precipitin reactions, 

 single and double diffusion in agar, complement fixation and immunoelectro- 

 phoresis. All of the tests confirm the identity of the chromatophore fragment 

 antigen and the various fractions cited. From these results it can be concluded that 

 the chromatophores are derived, at least in part, from material structurally similar 

 to that making up the cell wall, and that soluble intracellular protein is struc- 

 turally similar to the surface protein of chromatophores. A unique feature of this 

 technique as applied to a photo-active system is that the antigen is colored, thereby 

 simplifying application of the method. 



These studies indicate that immunochemical techniques can be extended as a 

 promising method for identifying active sites on the lipoprotein complex. In ad- 

 dition, the nature of the binding sites for chlorophyll and carotenoid can be in- 

 ferred by correlation of observations of changes in chlorophyll spectrum and de- 

 gree of antigenic activity as a function of proteolytic digestion by agents such as 

 trypsin, subtilin, etc. There are many other applications too numerous to men- 

 tion in this limited space. 



SIGNIFICANCE OF PHOTOPHOSPHORYLATION REACTION 



The similarities which exist between the bacterial chromatophores and the green 

 plant chloroplasts are such as to indicate that the same general mechanism is 

 operative in photometabolism in both types of systems. It appears that the only 

 essential difference between green plant and bacterial photosynthesis — namely, the 

 lack of an oxygen evolution system in the latter case — is also the only essential 



