INTRODUCTORY REMARKS 7 



porphyrin structure of the chlorophylls when the Mg and N atoms as well as 

 the side chains are omitted (Fig. 4). 



There is evidence for assuming that the carotenoids have special tasks in 

 photosynthesis. It has even been stated that they may take an active part 

 in the primary act of the photosynthetic process. Lynch and French (26) 

 observed that the Hill reaction is inhibited when the carotenoids are removed 

 from the chloroplasts by extraction. After the addition of /3-carotene 

 to such chloroplasts the Hill reaction can again be demonstrated. Fujimori 

 and Livingston (15) found that the carotenoids are as efficient as oxygen in 

 quenching the triplet state of chlorophyll a. However, for the time being 

 there is not sufficient evidence to attribute a primary role in photosynthesis to 

 the carotenoids. The findings of Sager and Zalokar (32) support the 

 hypothesis that the carotenoids are not essential for photosynthesis except 

 possibly in catalytic amounts. This is in agreement with Warburg's work 

 on the action of blue-green light and the role of the photosynthesis enzyme to 

 be discussed in Section B of Chapter 3. Nishimura and Takamatsu (28) 

 found that /3-carotene in various leaves — like chlorophyll — is bound to 

 protein, an important discovery which also confirmed Warburg's views on 

 the photosynthesis enzyme (see § 31). The group of carotenoids also includes 

 xanthophyll and related compounds. 



The light absorption of chlorophyll in the visible spectrum is relatively 

 great. The absorption curve of a solution of chlorophyll a in ethyl ether 

 shows one maximum in the red and another in the violet. In organic 

 solvents the pigment gives a characteristic fluorescence spectrum where — 

 as in the absorption spectrum — the position of the bands depends upon the 

 kind of solvent used. The addition of quinone, oxygen and some other 

 substances inhibits fluorescence to varying degrees, whereas removal of the 

 Mg atom has practically no influence. In vivo, chlorophyll shows very 

 little fluorescence (see § 1 1) and colloidal solutions of chlorophyll do not show 

 fluorescence at all (23). Warburg (46) pointed out that extracts of chlorophyll 

 in organic solvents should not be identified with the functioning chlorophyll 

 in the chloroplasts. In the study of photosynthesis distinction has to be made 

 between "dead" and "living" chlorophyll (see § 59). 



The carotenoids absorb light in the violet, showing two or three bands, 

 the positions of which vary according to the solvent used. 



TABLE 1 

 Conversion factors for chlorophyll concentrations 



