SOLUBLE PROTEIN- PIGMENT COMPLEXES FROM SPINACH CHLOROPLASTS 



Joseph S . Kahn 



In recent years there has been a growing interest in the iso- 

 lation of subunits of chloroplasts containing portions of their 

 photochemical and electron transport pathways. Such subunits 

 could aid in elucidating the pathway of electron flow in the 

 chloroplast, as well as provide a clue to the mechanism of the 

 photochemical reaction itself. One of the most difficult 

 aspects of this approach has been the isolation of photosynthetic 

 pigments in conjunction with the proteins with which they are 

 associated. The isolation of a soluble cytochrome c photo- 

 oxidase, and of a protein-chlorophyll complex which could be 

 bleached to produce three new pigments, have been reported (1,2). 

 Also, a protein-y4-carotene complex has been isolated from chloro- 

 plasts (3). Disruption of chloroplasts by sonication has 

 yielded small fragments which could be the catalyst for one of 

 the two light reactions required for photosynthesis (4). 



This report describes two soluble protein-pigment complexes 

 which were isolated and purified from spinach chloroplasts and 

 which, in combination, catalyze the photoreduction of ferri- 

 cyanide . 



A Soluble Protein-Chlorophyll Complex 



By fractional solubilization of chloroplast fragments with 

 Triton x-100 and chromatography on DEAE-cellulose in the presence 

 of Triton, a soluble protein-chlorophyll complex was isolated. 

 Details of the techniques have been reported elsewhere (5) . The 

 complex represents 3-8% of the total chlorophyll of the chloro- 

 plast and contains 0.8-1.2 mg protein/;amole chlorophyll. The 

 low-temperature spectrum of the complex reveals the chlorophyll 

 to be chlorophyll a. 



In order to avoid difficulties caused by chlorophyll bleaching, 

 and in order to increase the sensitivity of the assay, ferri- „ 

 cyanide reduction was measured with o-phenanthroline and the Fe 

 chelate of o-hydroxyethylene-diamine diphenyl acetate (Sequest- 

 rene 138 Fe of the Geigy Chemical Co.) (5). The protein- 



496 



