282 MARTIN D. KAMEN 



and which, as mentioned previously, is a pyridine-nucleotide linked haem 

 protein reductase. 



These results relating to the cytochrome content of the Chromatiiim 

 chromatophores are applicable generally to all photoactive particles, 

 whether of bacterial or plant origin. Surveys of all the typical species of 

 photosynthetic bacteria [28] and of a large variety of plants and algae [29, 

 30] reveal that, regardless of aerobic or anaerobic habit, these systems all 

 contain relatively large amounts of haem proteins. Further, although the 

 major component invariably is a cytochrome of the "c" type, no corre- 

 sponding oxidase of the "fl" type is found associated with chromatophores 

 or chloroplasts. Significant aspects of these findings have been discussed 

 sufficiently elsewhere [19, 31]. Let us proceed to the central topic of this 

 paper — a possible relation between haem protein content and the early 

 photochemistry of the photosynthetic process. 



The ultimate consequence of the photochemical act may be thought of 

 as the establishment of a voltage gap between two systems. This gap is 

 sufficiently large in the case of the green plants and algae so that one 

 system can operate at a "mid-point" potential reducing enough 

 (negative £"0) to drive reductive assimilation of CO., (and perhaps generate 

 ATP simultaneously) while the other can provide a sufficiently high 

 oxidizing "mid-point" (positive is^) potential eventually to liberate 

 oxygen from water. In bacteria, a small gap may be all that is necessary 

 because oxygen is not liberated during COg assimilation. The significance 

 of our question about a sufficient and necessary molecular composition 

 and placement, posed in our previous discussion, is that if we know what 

 molecules are present, their relative concentrations, and their disposition, 

 we may begin to develop and examine hypotheses for identifying reactants 

 in the primary photochemistry. In Chromatiiim chromatophores, Newton 

 and Newton [11] have shown that the major constituents present in both 

 chromatophores and chromatophore fragments include, in addition to the 

 photoactive pigments and the major gross fractions of protein, lipid, and 

 carbohydrate, components typical of a mitochondrial respiratory chain, 

 e.g. pyridine nucleotides, flavins, quinones, and cytochromes. Associated 

 with these compounds are a variety of enzyme activities typical of an 

 electron-transport system, as noted previously. 



In Chromatiiim chromatophores, there are, for every 20 bacterio- 

 chlorophyll molecules, 11 carotenoids, 1-5 haem protein, i flavin, and i 

 pyridine nucleotide. We have remarked that further fragmentation to 

 small particles results in the loss of a major part of the polysaccharides, 

 some protein, but less lipid, so that the fragmented particles became 

 relatively enriched in lipid. However, the haem protein content relative to 

 chlorophyll remains unchanged, both doubling relative to total protein 

 content. Thus, in the chromatophore fragment (which is still capable of 



