PIGMENT-PROTEIN SUSPENSIONS AND SOLUTIONS 385 



complex, and then dissolved the chlorophyll from the precipitate. Similar 

 extracts prepared from other plants were turbid and unstable. 



Lubimenko found that the aqueous complex contained not only the 

 chlorophyll but also the carotenoids of the leaves, and considered it as a 

 chemical compound which he called "natural chlorophyll." 



Noack (1927) also prepared a green extract by centrifuging triturates 

 of different leaves. These extracts were fluorescent, decomposed upon 

 heating above 70° C, and were precipitated by heavy metal salts and 

 ammonium sulfate. 



Price and Wyckoff (1938) and Loring, Osborne, and Wyckoff (1938) 

 obtained green aqueous solutions by the centrifugation of press juices 

 of cucumber and green pea leaves. The colored protein particles were 

 very heavy (molecular weight ~ 500,000, judging by the high velocity 

 of their precipitation in the ultracentrifuge). 



Stoll and Wiedemann (1938) prepared green aqueous extracts from 

 spinach, nettle, wheat, rye, grass, sunflower, and many other plants, by 

 grinding them at low temperature in distilled water, avoiding contact 

 with metal. Suspensions prepared from different leaves were similar, 

 and resembled living leaves in respect to spectrum, fluorescence, and 

 stability to light, oxygen, and carbonic acid. They could be freed by 

 centrifuging from larger cell fragments, and, by twice-repeated salting 

 out with ammonium sulfate, from different colorless and brown, water- 

 soluble admixtures. At 0° C, not much substance was lost by de- 

 naturation in the course of this purification. A final purification was 

 carried out by precipitation of the colored protein in a high-speed centri- 

 fuge (45,000 r.p.m.), and dialysis through a cellophane membrane into 

 distilled water. The product was designated by Stoll and Wiedemann 

 as "chloroplastin." 



The green colloidal "solution" of chloroplastin, obtained by re- 

 suspending the purified product in distilled water, remains stable for 

 months at pH 7.2-7.4, and 0.2° C. It is denatured by changes in pH, 

 drying, or warming. Light and air do not affect it — an illumination of 

 40,000 lux for 25 hours in contact with air caused no damage, although 

 this treatment would have destroyed completely any molecular or 

 colloidal solution of chlorophyll. No particles can be detected in chloro- 

 plastin suspensions under the microscope, even with powerful immersion 

 systems. In the ultramicroscope, the solutions sometimes appear 

 optically empty, but sometimes show particles engaged in a lively 

 Brownian motion. Stoll and Wiedemann considered these particles as 

 accidental agglomerations of the invisible "chloroplastin molecules." 

 Shaking with ether does not extract chlorophyll from these suspensions, 

 unless salts are added (the chloroplastin complex is easily broken by 

 salts, for example, sodium chloride). The purified, resuspended chloro- 



