CYTOCHROMES 167 



In applying this test to various rat tissues it was found that agree- 

 ment between animals was reasonably good; the order of activity 

 of the tissues was the same in all the rats studied. The average results 

 of the cytochrome c estimations in the tissues of ten rats are re- 

 corded in Table 2. 



Table 2.— Comparison of cytochrome oxidase and cytochrome c 

 activities of rat tissues 



(Reference 77) 



Oxidase Cytochrome c 



Units per 



mg. dry ' mg. per g. 



tissue dry tissue 



Heart 9.7 Heart 2.34 



Kidney 4.7 Kidney 1.36 



Brain 3.5 Skeletal muscle . 68 



Skeletal muscle 2.3 Brain 0.35 



Liver 1.7 Liver . 24 



Spleen 1.6 Spleen 0.21 



Lung 1.3 Lung 0.14 



Testis 1.1 Embryo (early) 0.03 



Diaphragm muscle 0.72 Embryo (late) 0.18 



Large intestine 0.36 Tumor R-256 0.02 



Embryo (early, late) 1.1 Tumor R-39 0.03 



Tumor R-256 2.9 Tumor spontaneous 0.01 



Tumor spontaneous 2.4 



Most striking is the low cytochrome c content of embryos and 

 the tumors studied. It may be noted that the cytochrome c content 

 of the embryos increases just before birth. With the present knowl- 

 edge of the importance of cytochrome c in respiration, the low c 

 content of these tissues may be at least one factor responsible for 

 the aerobic glycolysis of these tissues. 



Potter and Dubois (78) have likewise developed a micro method 

 for estimating cytochrome c, the actual deteiTnination being made 

 with a photoelectric spectrophotometer; the light absorption is 

 measured before and after specific enzymatic reduction with succi- 

 nate. The values they obtained with rat tissues are in remarkably 

 good agreement with those recorded by Stotz. They have found a 

 low c content in several tumors thus far studied. 



The manometric estimation of oxidase activity in rat tissues may 

 be carried out on ground dialyzed tissue in the presence of excess 

 cytochrome with hydroquinone as a substrate (77). Schultze (49) 

 uses in addition semicarbazide, which maintains a constant rate of 

 oxidation over a longer period, a helpful modification. 



