THE MECHANISM OF PHOTOSYNTHESIS 



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The observations on purple bacteria suggest that in the Hving cells 

 bacteriochlorophyll may occur as different pigment-protein compounds, 

 each characterized by a different infrared absorption maximum (Wassink 

 et at., 1939). Association of the pigment with protein is now generally 

 accepted as essential for photosynthesis. A function of the protein may 

 be to conduct the energy absorbed by the pigment to energy acceptors 

 acting chemically in photosynthesis. The pigment-protein complex from 

 green cells was called "phyllochlorin" (Mestre, 1930) or " chloroplastin " 

 (Stoll, 1936). The present writer proposed that any colored pigment- 

 protein complex from plant cells be called ''chromophyllin" and that the 

 photosynthetically active one from green plant cells be called "chloro- 

 phyllin" (Wassink, 1948b), a terminology related to that used by Engel- 



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(a) (b) 



Fig. 5-5. (a) Red absorption maximum of chlorophyll in Chlorella cells (curve 1) and 

 of the cell-free chlorophyllin (curve 2). (From Wassink, 1942, according to Katz and 

 Wassink, 1939.) 



(b) Infrared absorption maximum of bacteriochlorophyll in Chromatium, strain D, 

 cells (curve 1) and cell-free bacteriochlorophyllin (curve 2). {From Wassink, 1942, 

 according to Katz and Wassink, 1939.) 



mann (1883). Stoll and coworkers (Stoll and Wiedemann, 1939; Stoll 

 et al., 1941) showed that the chlorophyllin in suspension contains carote- 

 noids, probably the majority of the carotenoids present in the plastid in 

 the living state. This also holds for the spontaneously extruding as well 

 as for the artificially prepared chromophyllin from the purple bacteria; 

 these chromophyllins contain bacteriochlorophyll and red carotenoids. 



Blue-green algae, also, under certain conditions extrude a blue or 

 purple compound in much the same way as described for the purple 

 bacteria. This compound, phycocyanin, is a protein from which the 

 splitting of the chromophoric grouping is very difficult (Lemberg, 1928, 

 1930, 1933). The breaking of the bond between pigment and protein is 

 much easier in the chlorophyllin (and also in the bacteriochlorophyllin) 

 than it is in the phycocyanin. The spontaneous extrusion of phyco- 

 cyanin suggests that its protein differs from that of the chlorophyll- 

 carotenoid complex, which under similar conditions remains inside the 



