354 RADIATION BIOLOGY 



phyll protein has been obtained in crystalline form by Takashima (1952) 

 in H. Tamiya's laboratory. This crystalline material, dissolved in 50 per 

 cent a-picoline, is shown in Fig. Q-Sd in comparison with the suspension 

 of broken chloroplasts from which it was prepared. The carotenoids 

 have been removed, and, in addition, it is obvious from the shift in 

 position of the red peak that some changes in the structure of the chloro- 

 phyll complex have taken place. The position of the peak at 435 m/x is, 

 however, unaffected. What the relation may be between this crystalline 

 derivative and chlorophyll in its native state in living organisms has not 

 been determined. This is, however, the only chlorophyll-protein com- 

 plex which has been isolated free of carotenoids and which has been 

 crystallized. The crystals of this material remarkably resemble the 

 appearance of sea urchins, being composed of a ball-like mass with 

 numerous radial spikes. The molecular weight of this material was 

 found to be about 19,200, the composition being about two molecules of 

 chlorophyll per protein molecule. 



ABSORPTION SPECTRA 

 OF SOME PURIFIED CHLOROPLAST PIGMENTS 



Chlorophylls. For quantitative determinations of chlorophyll a and b 

 the measurement of the absorption in ether is preferable. The absorp- 

 tion curves of chlorophylls a and b in ether are presented in Chap. 7, 

 Fig. 7-6. The absorption spectra of chlorophylls a and b in methanol 

 are given in Fig. 6-4a. Although small amounts of water somewhat 

 influence the height and shape of these curves, they are, nevertheless, 

 very useful in the study of crude plant extracts in methanol. In addi- 

 tion, in Fig. 6-46 are given the curves for pheophytin a and b. Plant 

 extracts, unless prepared with great care, may contain some chlorophyll 

 that has been changed to pheophytin as a result of reaction with plant 

 acids during extraction. Figure 6-4 also shows the absorption curves in 

 methanol of chlorophyll c, found in dinoflagellates and brown algae, and 

 of chlorophyll d, which is present in red algae. The participation of 

 chlorophylls c and d in photosynthesis yet remains to be demonstrated. 



Carotenoids. Descriptions of the individual carotenoids have been 

 given by Strain (1949) with emphasis on the groups of plants in which 

 the different carotenoids are found. The detailed chemistry of carote- 

 noids is given by Karrer and Jucker (1950), and a monograph on the 

 xanthophylls has been pubhshed by Strain (1938). The question of the 

 function of carotenoids in various organisms, particularly in photosyn- 

 thesizing plants, has received a great deal of attention, although at pres- 

 ent the function of carotenoids in nonphotosynthetic organisms is not 

 known. The relation of a-carotene to vitamin A is the only obvious 

 importance of the group of compounds aside from their connection with 



