386 CHLOROPLASTS AND CHROMOPLASTS CHAP. 14 



plastin contained about 80% protein, 10-20% lipoids, and 5% pigments 

 (including chlorophyll a, chlorophyll h, carotene, and the carotenols, 

 in the same proportion as in the intact leaves). 



Preparations similar to those of Stoll and Wiedemann were obtained 

 by many other investigators. Katz and Wassink (1939) prepared them 

 by grinding unicellular green and blue algae (Chlorella and Oscillatoria). 

 Cataphoresis experiments showed that the particles of these suspensions 

 were negatively charged: they became positive in 0.002 normal hydro- 

 chloric acid. The isoelectric point was at or near 3.7 (confirmed by 

 Neish 1939). Fishman and Moyer (1942) studied the electrophoresis of 

 suspensions obtained by grinding of Aspidistra elatior and Phaseolus 

 vulgaris leaves. In agreement with the results of Stoll and Wiedemann, 

 they were found to be fluorescent and photostable, but temperature- 

 sensitive. The Brownian motion of the particles was clearly visible in 

 the dark field, and they were large enough to observe electrophoresis. 

 They were negatively charged. The isoelectric point was at pH 4.7 for 

 the suspension from Phaseolus (as against pH 4.22 for the cytoplasmic 

 proteins from the same source); that of Aspidistra was at a much lower 

 pH (~ 3.9). Moyer and Fishman (1943) found that the isoelectric 

 points of chloroplastic suspensions from ten species of legumes varied 

 between 4.6 and 5.0. 



Lubimenko, and Stoll and Wiedemann, had a tendency to stress the 

 "molecular" character of the protein-pigment complex: it was asserted 

 by them to be uniform in composition, and the size of its particles below 

 the limit of ultramicroscopic visibility, except for cases of agglomeration. 

 However, the observation of Fishman and Moyer that the particles are 

 generally visible in the dark field, and the fact — confirmed by Stoll and 

 Wiedemann — that they can be precipitated in an ordinary high-speed 

 centrifuge, places their size well above that of the largest known protein 

 molecules. Anson (1941) recalled the assertion of Lubimenko that 

 stable solutions can be obtained only with leaves of certain species, and 

 used one of them (Funkia) for his experiments; but he obtained merely 

 an opalescent suspension which was completely sedimented at 20,000 

 r.p.m. — that is, a suspension whose particles were much larger than the 

 gigantic molecules of the tobacco mosaic virus. 



The conclusion that the "chloroplastin solutions" obtained by the 

 grinding of leaves in distilled water are merely suspensions of particles of 

 comparatively large and nonuniform size was reached also by Smith 

 (1938, 1940, 1941), who studied the effect of different detergents on 

 extracts from Spinacia and Aspidistra, and found that "solutions" 

 obtained directly by grinding leaves under water produce no sharp sedi- 

 mentation boundary in the ultracentrifuge, and are usually large enough 

 to cause turbidity. (This applies also to preparations made from 



