THE MECHANISM OF PHOTOSYNTHESIS 



305 



the attachment to the chromophyllin for active carotenoids is different 

 from that for inactive ones. In the case of the fucoxanthin of diatoms, 

 evidence has been obtained indicative of a distinct binding of this active 

 carotenoid to protein. Fucoxanthin shows a shift in absorption upon 

 extraction, which is the main reason that the ethanol extract from the 

 brown diatoms is green. Also, cells warmed to 70°C turn green, which 



'^ 

 \ 



o 



• CHLOROPHYLL 

 ■ CHLOROPHYLL 







b 



o o o o o CHLOROPHYLL C 

 CHLOROPHYLL d 



o— o— o— o PROTOCHLOROPHYLL 

 —XX — XX— BACTERIOVIRIDIN 

 ,.*+***♦* BACTERIOCHLOROPHYLL 



IN METHANOL 



A 



IN ETHANOL 



300 



400 



700 



800 nyz 



500 600 



WAVE LENGTH 



Fig. 5-7. Absorption spectra of various chlorophylls. (Chlorophyll a, b, and c from 

 Strain and Manning, 1942; chlorophyll d from Manning and Strain, 1943; proto- 

 chlorophyll from Koski and Smith, 1948; bacterioviridin from Katz and Wassink, 1939; 

 bacteriochlorophyll from Manten, 1948). 



very probably has to be interpreted as a change in the chromophylhn 

 by denaturation of the protein (Wassink and Kersten, 1946-1948). 



The formulas of some major types of chlorophyll (including proto- 

 chlorophyll and bacterioviridin) and of bacteriochlorophyll (cf. Fischer 

 and Orth, 1940) are shown in Fig. 5-6. Some absorption spectra from 

 the literature are collected in Fig. 5-7. The chief absorption maxima of 

 the various chlorophylls are situated in much the same regions, but the 

 relative heights of the red maxima differ greatly. The maxima of bac- 

 teriochlorophylls are situated rather differently; the spectrum is much 

 wider (cf. Manten, 1948). This appears to be due to the hydrogenation 

 of a double bond between C3 and C4 in the pyrrol-methine nucleus of 



