THE LIGHT FACTOR IN PHOTOSYNTHESIS 



1031 



solvents. StoU stresses the fact that all the asymmetric carbon atoms of 

 chlorophyll carry labile hydrogen atoms and that these are responsible 

 for the ease of racemization and also for the fact that chlorophyll acts as a 

 hydrogen donor in the photosynthetic reaction. 



The principal carotenoid constituent of leaves, lutein, has a specific 

 rotation of [a]6438 = +145° in ethyl acetate; a-carotene, [aJeevs = +352° 

 in benzene; /3-carotene is optically inactive. 



The observation that photosynthesis in the brown and red algae 

 is more nearly equal for light of different spectral regions of equal intensity 

 than it is in the green plants (51, 21) is of particular interest for the corre- 

 lation of photosynthesis with the absorption spectra of the plants them- 

 selves and of their pigments. The pigment complex of these plants is 

 quite different from that of green plants. Besides chlorophyll, they 

 contain chromoproteins, the absorption spectra of which are comple- 

 mentary to the absorption spectra of the chlorophylls. The component 

 ratio of the chlorophyll differs in the brown and red algae from that 

 found in green plants (6). The brown algae also possess a carotenoid, 

 fucoxanthin (C40H56O6), which thus far has not been isolated from green 

 plants. 



The absorption bands of these pigments are (28, 61): 



I 



The fluorescence bands have been reported (6) as: 



Phycoerythrin X5790 A 



Blue-green phycocyanin X6550 A 



The pigment complex of the purple bacteria (bacteriopurpurin), 

 is different from that of the green plants (10). By observing the motility 

 of these organisms in a microspectrum they are seen to collect in sharp 

 bands which corresponded to the absorption bands of the bacteria 

 themselves. When culture flasks of these organisms are placed in the 

 light surrounded by a bath containing a filter of green organisms, the 

 purple bacteria thrive whereas green organisms fail to develop under 

 the same circumstances. This has been attributed to the fact that the 

 purple bacteria possess absorption bands which are complementary 

 to those of the green organisms, and that these organisms probably 

 assimilate in these spectral regions. The absorption bands have been 

 observed at the follow^ing wave-lengths: 9100 to 8900; 8700 to 8400; 

 8100 to 7850; 7600 to 7000; 6100 to 5750; 5400 to 5150; 5000 to 4850 (?); 

 4700 to 4550 A. 



