358 



PHOTOMECHANICAL CONSIDERATIONS 



AH, 



'Oxysome" Succ. 

 DPN- 



DPN 

 -fp- 



I~X 



fp 



b.Q.Fe 



Cu? 



DPN 



Bacterial 

 Quantasome' 



Fig. 1. Electron transfer and transport pathways in light- and 

 oxygen -induced reactions (ME-115), 



induced systems, namely, that the electrons, instead of flowing down a 

 thermodynamic gradient to water as in the oxygen-induced system, 

 are activated by the excited state of chlorophyll so that they leave 

 cytochrome and flow to an electron acceptor. 



Obviously, many structural similarities exist in the two systems, 

 and these similarities are emphasized in the various attempts to iso- 

 late their "elementary assemblies": the chromatophore or "quanta- 

 some" of the photosynthetic system (9), or the "elementary particle" 

 (10) or "oxysome" (7) of the oxygen- activated system. Electron micro- 

 graphic data of fine structure in mitochondria now appear to be the 

 most convincing evidence in favor of elementary structure. However, 

 an objective study of the actual sizes of the units involved strongly 

 suggests that fine structure of mitochondria is much more appro- 

 priately associated with the respiratory carriers themselves and their 

 oxidative phosphorylation cofactors than with the complete unit of 

 electron transport and phosphorylation. In fact, we envisage this fine 

 structure to represent a continuum of bound, yet mobile, carriers in- 

 teracting by rotational and collisional motions to transport electrons 

 from substrate to oxygen with attendant phosphorylation (7). In this 

 symposium a similar view of a continuum membrane structure is 

 also suggested and it will be interesting to determine whether or not 

 the chromatophore or quantasome shows a similar type of fine struc- 

 ture suggesting electron carrier mobility. With the possibility in mind 



