DISULFIDE PHO TOR EDUCTION 313 



are protected against inactivation by preincubation in light with an 

 electron donor system. 



DISCUSSION 



The inclination is to interpret these observations as a result of 

 light-induced conformational changes taking place in the bacterial 

 chromatophore during induction. The nature of the interactions is sug- 

 gested by the types of reagents inducing and eliminating the lag period. 

 Salts, which would be expected to strengthen hydrophobic interactions 

 among nonpolar chromatophore components (18), eliminate the lag. 

 Nonionic solutes and detergents, which would weaken hydrophobic 

 interactions, extend or produce induction. These results have opened 

 up a new area of research currently under investigation. 



Some of our earlier immunochemical studies, and the intriguing 

 observations of Tuttle and Gest (19), have suggested that bacterial 

 chromatophores are associated with the cytoplasmic membrane in R. 

 nibnim. If so, then one might expect light-induced electron flow to 

 alter the mechanical properties of the membrane and its permeability. 

 Indications of this are already provided by recent experiments of 

 Bose, Gest, and Ormerod (20), Further work, relevant to our own work 

 on disulfides, shows that membrane transport processes, both in the 

 mitochondrial (21) and toad bladder systems (22), are closely linked 

 to thiol-disulfide interactions in the membranes involved. If these 

 phenomena are all interrelated in the membranous bacterial chroma- 

 tophore, then the induction period in chromatophore-photochemical- 

 redox reactions might indicate a relationship between the mechanical 

 properties of the membrane and photochemical electron transport in 

 this subcellular system. Such a relationship has already been indicated 

 in work on oxidative phosphorylation systems and predicted to exist in 

 all phosphorylating systems by the elegant theoretical work of Mitchell 

 (23). 



REFERENCES 



Newton, J. W., and Levinc, L,, Immunochemical studies on the photoactive 

 subcellular particles from Chromatin}}}. A)-cI). Biochc}}}. Biophys., S3, 456 

 (1959), 



Newton, J, W., Macromolecular variation in the chromatophores of the 

 photosynthetic bacterium /?/?0(fos/)/n7Z»;;? rubrum. Biochim. Biophys. Acta, 

 42. 34 "(1960). 



Newton, J, VV,, Immunochemical studies on disulfide bonding in the photo- 

 chemical apparatus of Rhodospirilhu}} nibnim. Biochim. Biophys. Acta, 

 58, 474 (1962). 



