REACTION CENTERS IN PHOTOSYNTHESIS 

 TABLE 1. 



Reactions suggested by light -induced absorption spectrum changes 

 in plwtosynthetic bacteria. 



381 



Type 



Substance 



A O. D. 



Reaction 



B 



P870-P890* 



one or more 

 cytochromes 



C ubiquinone 



D carotenoids 



bacteriochlorophyll ? 

 P870-P890? 



oxidized P870- 

 P890? 



Bleaching centered at the long-wave oxidation 

 absorption band of BChl (870-890 



Blue-shift of soret band, bleaching oxidation 



of OL and y5 bands. 



Bleaching centered at 270-275 m//. reduction 



Bleaching and red-shift of absorption 

 bands. 



Bleaching at 605 and 380 m/i. 

 Blue-shift of bands at 800, 590, and 

 375 m^. 



Bands appear at 435, 720, and 1000- oxidation 

 1250 mfl. 



P870 in Rhodopseudo monas 

 Chromatium (see text). 



spheroides ; P890 in Rlw do spirillum rubrum and 



The light reactions listed in Table 1 as Types E and F accompany 

 the P870-890 reaction, in fixed proportions and with the same kineticsS 

 (26,27). It is not clear to what extent these reactions are additional 

 manifestations of the P870-890 reaction. The Type F reaction is pro- 

 duced by chemical oxidation as well as by light, in the same way as 

 the bleaching at 870-890 m/y (27). Of the events listed as Type E, only 

 the blue- shift at 800 m/i has been shown clearly to be duplicated by 

 chemical oxidation. Moreover, this blue-shift can be produced chemi- 

 cally in varying proportion to the bleaching at 870-890 m/i, depending 

 on the oxidation potential (25). The reactions of Types E and F are 

 interpreted provisionally as follows. The bleaching at 380, 605, and 

 870-890 mji reflects the bleaching of P870 orP890, this pigment being 

 a specialized component of BChl in the chromatophore. The bands 

 appearing at 435, 720, and 1000 to 1250 m/y (Type F) belong to oxidized 

 P870 or P890. It should be noted that each of these bands represents 

 an energy level about 0.4 electron volts below that of a BChl band. 



5 There is some confusion about the broad light-induced absorption band at 

 435 mn; more than one substance may be involved (31,34). In washed or dried 

 chromatophores this effect represents a single reaction showing the same 

 kinetics as the P870-890 reaction (26,27). 



