CYTOCHROME SYSTEMS 



45 



out oxidation mechanisms of the cytochrome type. It is 

 possible that some other carrier might take the place of 

 cytochrome but the only one of these organisms which is 

 known to produce a pigment which can be reversibly oxidised 

 and reduced, other than cytochrome, is Ps. jpyocyanea 

 {Ps. aeruginosa). This elaborates a blue pigment, pyocyanine, 

 which is capable of acting as a hydrogen- carrier with certain 

 dehydrogenase systems when tested in vitro. This organism 

 has, however, a full complement of cytochrome components. 



TABLE IV 

 Distribution of CYTOcimoME Components in Bacteria 



The organisms devoid of cytochrome are either strict 

 anaerobes such as the Clostridia, or microaerophilic such as the 

 Streptococci or Lactobacilli; this suggests that the absence 

 of cytochrome components leads to the inability of these cells 

 to utiHse oxygen. Isolated dehydrogenase systems can be 

 made to react in vitro by replacing,^ cytochrome with certain 

 "redox" indicators such as methylene blue or cresyl blue; 

 the dehydrogenase catalyses the transference of hydrogen 

 from substrate to the dye, and the reduced dye is autoxidisable. 

 When cytochrome is replaced in this way the final product 

 of the oxidation is HgOg and not HgO, so that the complete 



