ayS MARTIN D. KAMKN 



chromatophore is a minimal structure. The usual experimental approach 

 is to fragment cells to photoactive particles and then continue fragmenta- 

 tion until some photochemical process, such as the Hill reaction, or photo- 

 phosphorvlation, is no longer supported by the particle preparation 

 obtained. Then, re-activation by the addition of external factors is used to 

 define the biochemical system. Unfortunately, such an approach merely 

 defines a system that can work, but not necessarilv one that functions in 

 normal photosynthesis. As an example, we may recall the remarkable 

 activation of photophosphorylation by phenazine methosulphate, first seen 

 in bacterial chromatophore preparations [2, 3, 4]. 



A refinement on this methodology is to examine soluble factors 

 originally present in the intact cell, or chromatophore, and which were 

 removed during fractionation. A number of investigators have found that 

 the washings from chromatophores and chloroplasts contain activators for 

 photophosphorylation, but the nature of these factors remains obscure. 

 The soluble system obtained by washing fragmented chromatophores is 

 complex, containing numerous enzvmes associated with activities such as 

 adenylate kinase, exchange of ATP with inorganic P, nucleotidase, nucleic 

 acid depolvmerase, catalase and peroxidase, etc. In addition, there are non- 

 specific reductants, as well as fiavins, quinones and haem proteins which 

 have been dissociated from their binding sites in the chromatophore. 

 Dr. Horio and I have found recentlv (unpublished) that thoroughly 

 washed chromatophores from RhoduspirilliDn riibnim, which are wholly 

 inactive in photophosphorylation, can be reactivated by addition of the 

 purified haem protein, a pure vellow flavin enzyme which is a pyridine 

 nuclcotidc-linked haem reductase, and a \olatile reductant obtained by 

 distillation of acetone extracts of fresh cells. These results are an improve- 

 ment on those previouslv obtained using crude extracts, or artificial 

 electron transport mediators like phenazine methosulphate, because they 

 demonstrate the ability of single factors originally present in the chro- 

 matophore to participate in the normal metabolic process.* 



Other approaches can be based on synthesis rather than breakdown of 

 the photochemical apparatus. Possible methods include extraction of pre- 

 cursor particles from colourless mutants, physical treatments of normal 

 cells which interfere with chloroplast or chromatophore development (e.g. 

 heat [5], u.v. irradiation, variation in oxygen tension [6], heterotrophic 

 growth conditions [6], etc.). Immunochemical approaches have been 

 described in which sera specifically directed against components extracted 

 from light-grown and dark-grown bacterial svstems have been prepared 

 [7, 8]. 



* H. Baltscheffsky {Biochim. hiopliys. Acta 41, i (i960)) has published recently 

 results of studies of this type implicating flavin adenine dinucleotide as an inter- 

 mediate in electron transport coupled to photophosphorylation. 



