388 CHLOROPLASTS AND CHROMOPLASTS CHAP. 14 



Differences between the absorption spectra of different leaves have 

 led Lubimenko (1927) to believe that they contain slightly different — 

 perhaps isomeric — green pigments; however, many of these variations 

 may be caused by scattering and by varying proportions of components 

 a and 6 (Chapter 23, Vol. II). If, however, it should be proved that 

 genuine spectroscopic differences exist between the green cells of different 

 species, one should think first of association with different proteins 

 (rather than variations in the structure of the pigment molecule). This 

 view is supported by observations on the spectrum of bacteriochlorophyll- 

 protein extracts {cf. Chapter 22, Vol. II) and on the isoelectric points of 

 suspended chloroplast matter from different plants {cf. above, page 386). 



Mention should be made here of attempts to prepare artificial protein- 

 chlorophyll complexes from chlorophyll solutions in organic solvents. 

 Eisler and Portheim (1922) precipitated chlorophyll from alcoholic 

 extracts with horse serum. The green precipitate was water-soluble; 

 its spectrum was described as "similar to that of chlorophyll in the 

 leaves." It was slightly fluorescent (according to Eisler and Portheim 

 1923, it was even photosynthetically active!). Noack (1927) adsorbed 

 chlorophyll on proteins (albumin, casein, legumin, hordenin, and clupein 

 sulfate), and on peptones. Some of these precipitates were weakly 

 fluorescent, but Seybold and Egle (1940), who repeated Noack's experi- 

 ments, suspected that their fluorescence was a sign of the presence of 

 lipoid impurities {cf. Chapter 24, Vol. II). 



In all of Smith's experiments (1940-1941), the carotenoids apparently 

 followed chlorophyll, thus supporting Lubimenko's view that the natural 

 complex (" chlorophylle naturelle") contains not only chlorophyll and 

 protein but also the yellow pigments. However, Lubimenko's contention 

 that the carotenoids do not exist as such in the natural state (because 

 their absorption peaks are absent in the leaf spectrum) must be rejected. 

 Not only is it a priori implausible, but the absorption maxima of the 

 carotenoids actually can be recognized in many absorption curves of 

 green leaves and algae, and particularly clearly in those of purple bac- 

 teria {cf. numerous figures in Chapter 22, Vol. II). 



The association of hacteriochlorophyll in purple bacteria with proteins 

 has been proved by experiments similar to those described above for 

 the higher plants. Levy, Tessier, and Wurmser (1925) obtained aqueous 

 extracts of a colored protein by grinding purple bacteria {Chromatium) ; 

 while French (1938, 1940) used ultrasonic waves to break the bacteria 

 {Streptococcus varians, Rhodo spirillum ruhrum, Rhodovibrio, and Phaeo- 

 monas) and to release their cell content. The mixture obtained in this 

 way was separated by centrifugation from cell fragments, and a clear 

 colloidal solution remained which contained both the hacteriochlorophyll 

 and the bacterial carotenoids, together with the proteins. The absorp- 

 tion spectrum of the extract was very similar to that of intact bacteria. 



