168 A SYMPOSIUM ON RESPIRATORY ENZYMES 



The distribution of oxidase in rat tissues is also illustrated in Table 

 2. Perhaps the most interesting thing about these data is the fact 

 that the oxidase activity of the tissues parallels quite closely their 

 cytochrome c content, although in the case of the tumors and em- 

 bryonic tissue there is no lack of cytochrome oxidase. This paral- 

 lelism may indicate a close chemical similarity between, or common 

 origin of, cytochrome c and cytochrome oxidase. 



A decrease in oxidase activity has been noted in various tissues 

 of the rat in anemia (49, 50) and in guinea pig tissues during acute 

 scurvy (79). 



Physiological Functioning of the Cytochrome System 



Flexner and Stiehler (80, 81) have made some very interesting 

 observations on the funct. nal development of the cytochrome sys- 

 tem. By histochemical methods they studied the changes in the 

 chorioid plexus of the fetal p'g, especially during the phase when 

 the spinal fluid changes from an ultra-filtrate to a secretion. Oxidase 

 activity was measured by blue-staining with dimethyl p-phenylene- 

 diamine and alpha-naphthol, a test which of course measures the 

 combined oxidase and cytochrome activity. Oxidation-reduction 

 potentials were estimated by introduction of oxidation-reduction in- 

 dicators intravascularly or supravitally. It was found that previous 

 to the secretory phase the concentration of "indophenol oxidase" 

 was the same in the epithelium and stroma and that there was no 

 potential difference between the two. In the secretory phase, how- 

 ever, the oxidase was concentrated in the epithelium and a poten- 

 tial difference developed, more positive in the epithelium. It was 

 concluded that the functional changes occurring with the onset of 

 secretion are correlated with the potential difference set up as a 

 result of the selective development of the oxidase (cytochrome) sys- 

 tem in the epithelium. The selective transference of dyes across the 

 secretory plexus was abolished by cyanide, and this was associated 

 with a loss of the potential difference between epithelium and 

 stroma. 



Flexner, Flexner, and Straus (82) have likewise studied the cyto- 

 chrome system in the cerebral cortex of the fetal pig. During the 

 first half of gestation p-phenylenediamine was not actively oxidized, 

 but during the second half an active oxidation system was present. 

 Employing the test for cytochrome oxidase (using excess cyto- 

 chrome c), they found that there was no lack of oxidase in any 

 phase of gestation and hence the change in p-phenylenediamine 



