160 A SYMPOSIUM ON RESPIRATORY ENZYMES 



the regeneration of cytochrome oxidase in the bone marrow of 

 anemic rats was extremely rapid following administration of copper. 

 Important as these findings are, they do not constitute proof that 

 cytochrome oxidase contains the copper any more than similar find- 

 ings with hemoglobin regeneration. 



Graubard (51) claims actually to have isolated a water-soluble 

 cytochrome oxidase from uterus. It is very labile and its action is 

 inhibited by copper inhibitors. He therefore claims that at least this 

 oxidase contains copper as the active metal. Certainly any claims 

 for the identity of a water-soluble or copper-containing oxidase with 

 cytochrome oxidase must be supported by many experiments giving 

 evidence that the material conforms with the existing definition of 

 cytochrome oxidase. 



The work of Altschul, Abrams, and Hogness (52, 53) in connec- 

 tion with the oxidase is of particular interest. They first reported 

 the isolation from yeast of a soluble cytochrome oxidase which 

 aerobically oxidized cytochrome c, and which was inhibited by 

 cyanide and carbon monoxide. Upon concentration, it was noted, 

 the activity of the enzyme was inhibited by catalase. It was then 

 found that during reduction of the substrate, cytochrome c, hydro- 

 gen peroxide was produced as a contaminant and oxidation was 

 actually a catalyzed oxidation by peroxide. This enzyme, being 

 specific, is now called cytochrome c peroxidase. Because so little is 

 known about the physiological mechanism of the aerobic oxidation 

 of the cytochromes and of the function of hydrogen peroxide, this 

 very active enzyme may. be of no small importance physiologically. 



From the standpoint of isolation, therefore, we still have only 

 cytochrome c. The other cytochromes and the oxidase are still as- 

 sociated with insoluble particles and have resisted separation. The 

 usual opalescent alkaline phosphate extract of heart muscle, which 

 contains these substances, has been the subject of a physico-chemical 

 investigation by Stern (54). Observations of this material, in the 

 ultracentrifuge and electrophoresis reveal properties similar to those 

 of other macro-molecular materials, such as fractions from Rous 

 chicken sarcomata. Such a dispersed suspension of particles con- 

 tains lipids, nucleic acid, hemin, and other constituents. Stern feels 

 that it is largely a matter of definition whether such a "mono- 

 dispersed" suspension should be called a mechanical dispersion or a 

 true solution, and he predicts that when the individual components 

 are isolated they will no longer display their characteristic biological 

 orientation. This view does not and should not discourage attempts 



