124 THE BACTERIAL PHOTOCHEMICAL APPARATUS 



transfer carriers involved in photophosphorylation are significantly 

 disturbed by disruption of the native structure. Thus, optimal phos- 

 phorylation by isolated pigmented particles is observed only if the 

 overall redox potential is experimentally adjusted to a favorable 

 region by addition of suitable reductants or "redox buffers" (9,10). 



The process of photochemical H2 evolution apparently is even more 

 dependent on maintenance of in vivo structural integrity. Despite many 

 attempts, this reaction has not yet been definitively demonstrated in a 

 cell-free system using components exclusively derived from active 

 cells of photosynthetic bacteria. In this connection, it is noteworthy 

 that conversion of intact cells of R. rubrum to protoplasts using the 

 lysozyme technique causes almost complete loss of H2- evolution 

 activity (3). This could evidently be due to a direct inhibitory effect 

 of lysozyme or to loss of a required enzyme, or cofactor, from the 

 protoplasts. It is also conceivable that a relatively minor disturbance 

 of a delicate organizational state may be responsible for the disappear- 

 ance of activity. 



Although pigmented particles from R. ruhnim catalyze light- 

 dependent phosphorylation and certain oxidation- reduction reactions, 

 it seems possible that the properties of such particulate fragments 

 may be substantially modified by spontaneous architectural changes 

 which occur during their release from the cell. For example, struc- 

 tural lipids or lipoproteins organized in some sort of membranous 

 fabric may envelop, or partially overlay, normally accessible enzy- 

 matic components. This possibility is suggested by the effects of de- 

 oxycholate and other surface active agents on hydrogenase activities 

 of pigmented particle preparations. As shown in Fig. 1, lipid-dispersing 

 agents can cause marked acceleration of hydrogenase activity with an 

 artificial electron acceptor (activity with ferricyanide is also stimu- 

 lated). Similarly, hydrogenase activity of R. rubrum particles with 

 FMN or FAD is completely dependent on the presence of deoxycholate 

 or sodium lauryl sulfate (11). 



CONCLUSIONS 



The data now available from experiments with photosynthetic bac- 

 teria and previous experience with other complex particulate systems 

 indicate the desirability of exploring the photo- and biochemistry of 

 bacterial photosynthesis in subcellular preparations produced by 

 milder methods of cell rupture than are usually employed. Ideally, 

 one could hope to develop procedures which preserve the native sur- 

 face structures (cell "envelope" or "hull") and intracytoplasmic mem- 

 branes essentially intact but which effectively eliminate the perme- 



