122 THE BACTERIAL PHOTOCHEMICAL APPARATUS 



at low centrifugal force. As would be expected, washed "ghost" prep- 

 arations photophosphorylate ADP when supplemented with appropriate 

 cof actors (4). 



Pigmented membranous structures which catalyze photophosphory- 

 lation can also be obtained by disrupting cells of R. rubrum through 

 the sequential action of lysozyme and polymyxin B, in the absence of 

 an osmotic stabilizer (4), Polymyxin B is believed to react with lipid 

 components of the cytoplasmic membrane of sensitive Gram-negative 

 bacteria, causing disorganization of the membrane and an attendant 

 loss of specific permeability properties (5), It is significant that the 

 structures produced by the action of lysozyme + polymyxin Bon/?. 

 rubrum cells do not contain the large opaque granules characteristi- 

 cally seen in this organism when it is grown in certain media. This 

 observation reinforced the conclusion (4) that retention of the pigment 

 system in the "ghosts" was not due to physical entrapment of "chro- 

 matophores" by a limiting (damaged) membrane, "Chromatophores," 

 however, are readily released when the relatively fragile protoplasts 

 or "ghosts" are further disintegrated, e.g., by shaking with Ballotini 

 beads in the Mickle apparatus or by exposure to surface- active agents 

 such as sodium lauryl sulfate (4), 



The results briefly summarized above were the first indications^ 

 that the system of pigments and electron carriers responsible for 

 photochemical generation of ATP in R. rubrum is normally integrated 

 with the cytoplasmic membrane or intracytoplasmic extensions of the 

 membrane. This conception (3,4) received additional support from a 

 cytological investigation by Giesbrecht and Drews (7) with another 

 species oi Rhodospirillmn (molischianum) ; their electron micrographs 

 indicate that "chromatophores" ariseby invagination of the cytoplasmic 

 membrane and may, in fact, remain attached to the latter by tubular 

 stalks, A recent study (8) with R. nibnim has provided similar cyto- 

 logical evidence for an association of the photochemical apparatus 

 with the cytoplasmic membrane. 



It is well known that the properties of "particulate" enzymes can 

 be greatly influenced by the state of the structure with which they are 

 combined. Accordingly, in a photosynthetic bacterium such as R. 

 rubrum, disengagement of the pigment system and its associated 

 catalysts from the complex in vivo matrix might be expected to result 

 in significant alteration— or even total loss— of certain biochemical 

 properties (4). It appears that the normal redox balances of electron 



3 Immunochemical studies conducted with ChrojuatiH in at about the same time 

 by J. W. Newton (6) led him to conclude that "the photosynthetic apparatus of 

 purple bacteria is not necessarily a unique, discrete intracellular entity, since 

 it contains macromolecular configurations common to the cell surface on one 

 hand and certain 'intracellular' proteins on the other. It seems advisable, 

 therefore, provisionally to consider it a part of a more complex organizational 

 state within the cell." 



