PHOTOSYNTHETIC PHOSPHORYLATION I 07 



that the phosphorylated acceptor of carbon dioxide is considered to be ribulose 

 diphosphate (7) formed by reaction of this Hght-generated ATP with ribulose 

 phosphate (15, 24), we have the formulation tor the biochemical process of car- 

 bon dioxide fixation assumed at present to be operative in photosynthesis. 



CHARACTERISTICS OF PHOTOPHOSPHORVLATION IN CHROMATOPHORE PREPARATIONS 



Properties of Chromatophores. The photo-active subcellular particles in which 

 coupled phosphorylation occurs, trom any given species of the photosynthetic 

 bacteria, appear to be very similar or identical to those obtained from any 

 other species, at least as regards gross morphology and chemical composition. 

 Those from R. rubrum, first noted by Schachman, Pardee and Stanier (27), have 

 been described as spherical bodies ranging in size from 50 to 200 millimicrons (3, 

 II, 12). They may be obtained in a variety of ways; e.g., extraction of cells dis- 

 rupted by grinding with alumina, sonication, etc., followed usually by differential 

 centrifugation. With increasing fragmentation of the cells, the percentage of lipid 

 in the chromatophores rises to over 50 per cent of the dry weight, the remainder 

 being mainly protein. 



Similar results are obtained using Chromatin m. When sonication is prolonged, 

 fragmentation of the Chromatium chromatophores results, accompanied by the 

 loss of polysaccharide and small quantities of protein. The chromatophore frag- 

 ments appear to be uniform in size, in the range 20-40 millimicrons in diameter, 

 and are essentially phospholipoprotein in nature; they contain all the chlorophyll 

 and most of the carotenoid and cytochrome components of the original intact 

 cell. Thus, per milligram of protein, Newton and Newton (21) find in the 

 chromatophore fragments, in millimicromoles each: 40 chlorophyll, 17 carotenoid, 

 2.75 cytochrome (lumped and determined as pyridine hemochromogen), 0.5 flavin 

 and 0.9 pyridine nucleotide (21). The corresponding values for intact chromato- 

 phores are 20, 11, 1.48, i.o, and 1.2. 



It is seen that the chlorophyll and cytochrome remain bound tenaciously to the 

 particles, while other components are lost to a certain extent. Co-factors for the 

 photophosphorylation reaction are apparently also lost, because the fragments ex- 

 hibit only 5-10' '( of the specific reaction rate given by intact chromatophores (20). 

 Similar findings have been reported with washed R. rubrum chromatophores (11) 

 and spinach chloroplasts (2, 6). 



An interesting finding with the Chronicitinni chromatophore fragments is that 

 all the basic moiety of the phospholipid is accounted for as ethanolamine. This, 

 taken with the finding of equimolar amounts of ethanolamine, phosphate and 

 glycerol indicates the presence of a considerable amount of ethanolamine phos- 

 phatidic acid (21 ). 



