38 THE BACTERIAL PHOTOCHEMICAL APPARATUS 



TABLE 2 



Iron porphyrins in photosynthetic bacteria 



Organism Iron porphyrin contributed by 



Cytochrome b Cytochrome c RHP Catalase 



Values are calculated from the data of Clayton (12), Geller (13) and Bartsch 

 & Kamen (14), and are expressed as m/imoles of iron porphyrin/mg dry wt of 

 cells. 



the dark instead of photosynthetically synthesize little or no bacterio- 

 chlorophyll and under these circumstances the hemoproteins become 

 the major tetrapyrroles of the cells. Though there is a notable rise in 

 the catalase, particularly in Rps. spheroides , the total tetrapyrrole 

 does not approach the level found in light-grown cells (Table 2), It is 

 clear, therefore, that the main business of the tetrapyrrole-forming 

 machinery in photosynthetic organisms is directed towards making 

 chlorophylls. 



Porphyrins and derivatives. 



In his classical monograph on the Athiorhodaceae, van Niel (15) 

 observed that some species of Rhodopseudonionas excreted apink pig- 

 ment with absorption bands at 610, 565, and 535 m^. This was later 

 identified as a mixture of free porphyrins, coproporphyrin IE (Fig. 2) 

 being the major component, and is commonly found in the medium of 

 stationary phase cultures (16). The amount of porphyrin varies with 

 the species and strain and is most marked under conditions of iron 

 deficiency. There is an inverse relation between the amount of por- 

 phyrin accumulated and the concentration of bacteriochlorophyll in the 

 cells, the latter being favored by addition of iron (16). 



When oxygen is rigidly excluded from cultures of Athiorhodaceae, 

 colorless porphyrinogens (Fig, 2) accumulate which are converted to 

 porphyrins by autooxidation in the presence of air (17), 



