THE CHLOROPLAST 103 



chloiophvll molecule and other metals associated with chloroplast. 

 These chloroplastin particles are of the same order of size as those 

 found in the fixed dense lamellae of some chloroplasts; also they 

 could be considered similar to chromatophores. Therefore, it is 

 suggestive that chloroplastin is physiologically active, since the 

 chloroph\ll complex remains oriented in the digitonin micellar 

 particles. These particles could contain from 16 to 32 chlorophyll 

 molecules on the surface, as depicted by Frey-Wyssling ( 1957 ) . 

 The number of molecules that could be packed into this space would 

 be doubled if the chlorophylls were tilted on an angle of 45°, as 

 previously suggested. Such pigment molecules oriented in the dig- 

 itonin micelle particles could then be the active "photosynthetic 

 units." (See Fig. 6 for electron micrograph of Euglcna chloroplast 

 and chloroplastin. ) 



X-RAY Diffraction. Chlorophyll a has been shown to crystallize 

 out in thin sheets ^50 A thick, perhaps corresponding to bimolecular 

 layers of chlorophyll. The crystallized chlorophyll molecules occupy 

 an area of ~ 106 A-, and x-ray diffraction patterns obtained from 

 these crystals show strong bands at 7.6 A and 4 A (Jacob ct al., 

 1954). X-ray diffraction pictures were obtained by Belavtseva 

 (1957) from crystallized chlorophyll a plus h, prepared by petro- 

 leum ether extraction in Krasnovskii's laboratory. These patterns 

 showed a strong band at 7.68 A, with average bands at 4.22, 4.06, 

 3.66, 2.78, and 2.44 A, and weak bands at 2.05, 1.83, and 1.62 A. 



X-ray diffraction patterns were prepared at the Mellon Institute 

 for chloroplastin solutions and for chloroplastin films on glass slides. 

 For the solution, strong bands were found at 3.4 to 2.9 A and another 

 at 2.3 to 2.1 A; for the film, a broad band from 5.3 to 3.9 A was ob- 

 tained, with weak lines at 3.35, 2.13, 2.02, 1.82, 1.77, and 1.57 A. 

 These numbers are interplanar spacings. It is difficult at present to 

 interpret these bands; however, the 4 A band and some of the other 

 lines of chloroplastin in dried films approximate those for the crystal- 

 lized chlorophyll. 



Molecular Weight. Previously suggested molecular weights for 

 chloroplastin have been calculated for leaf extracts (spinach and 

 Aspidistra) prepared in a similar manner with digitonin. These 

 calculations, made from sedimentation rates in the analytical ultra- 

 centrifuge, give a molecular weight of the order of 265,000 ( Smith, 

 1941a, 1941b, 1941c). This is a high estimate, due in part to the 



