Particles in Photosyiithetic Phosphorylation^ 



MARTIN D. KAMEN and JACK W. NEWTON 



Brandeis University 

 Walt ham, Massachusetts 



THE DIVERSITY OF PHOTosYNTHETic TISSUES, ranging from anaerobic photo- 

 synthetic bacteria to the aerobic higher green plants, may be correlated with 

 a hierarchy of photo-active subcellular particles. These particles range in size from 

 those encountered in bacteria and some blue-green algae — so-called 'chromato- 

 phores' in bacteria and 'grana' in the algae — to relatively enormous chloroplasts 

 in some green plants. Chromatophores are spherical or semispherical bodies which 

 can be as small as 20-40 millimicrons in diameter, while chloroplasts are varie- 

 gated and often up to two orders of magnitude greater in linear dimensions. 

 Grana are usually disc-shaped and intermediate in size between chromatophores 

 and chloroplasts. They can occur as components or as individual entities. 



Considerable work has been done on the structure of chloroplasts and 

 grana (28). Chloroplasts in higher plants are generally ellipsoidal, typical di- 

 mensions in unicellular algae being 4-6 microns in diameter and 0.5-1 micron 

 thick. They can exhibit a variety of forms. Usually a laminar pattern is seen in 

 grana, indicating a structure consisting of 20-30 thin disc-shaped plates in a 

 stack. These platelets are probably protein discs about 10 millimicrons thick which 

 can carry one or more complete layers of chlorophyll intermixed with other com- 

 ponents of the photo-active system such as carotenoids, pyridine nucleotides, heme 

 proteins, etc. Generally, the grana are embedded in unpigmented lipoproteins — 

 so-called 'stroma' — which are probably the locus for enzymes involved in second- 

 ary functions such as COo assimilation, phosphate transfer, protein and lipid 

 synthesis, etc. 



Nothing is known about the fine structure of bacterial chromatophores but it 

 is reasonable to suppose they are similar to small grana such as those found in 

 blue-green algae. In fact, if we neglect the specification of a nucleus, a cell like the 

 anaerobic sulfur bacterium Chromatium can be considered as analogous to a 

 chloroplast, the chromatophores filling the role of grana and the extrachromato- 

 phore material that of the stroma. Recently, electron microscope pictures of 



^ Publication No. 21, (iraiiuate Department of Biochemistry, Brandeis University. Many of 

 the researches describeil in this paper were made possible by financial support from the 

 National Science Foundation, the C. F. Kettering Foundation and the National Institutes of 

 Health. 



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