Cytochrome Oxidases o/ Pseudomonas Aeruginosa 311 



where the thick arrows indicate an electron-transferring pathway of greater 

 physiological possibihty than the slender ones. The box indicates that the 

 enzymic protein of P-cytochrome oxidase has at least two different kinds of 

 haems, and is capable of displaying cytochrome oxidase activity in the 

 absence of any externally added respiratory components. In spite of the fact 

 that some parts of the absorption spectrum of P-cytochrome oxidase are very 

 similar to the a-, /5- and y- absorption bands of P-cytochrome-551 and 

 P-cytochrome-554, all attempts to split such a c-type cytochrome from native 

 P-cytochrome oxidase have failed. 



REFERENCES 



Barrett, J. (1956). Biochem. J. 64, 626. 



Chance, B. (1953). /. biol. Chem. 202, 383. 



FujiTA, A. & KoDAMA, T. (1934). Biochem. Z. 273, 186. 



Green, D. E. & Brosteaux, B. (1936). Biochem. J. 30, 1489. 



HiGASHi, T. (1958). J. Biocliem. Tokyo 45, 785. 



Horio, T. (1958a). /. Biocliem. Tol<yo 45, 197. 



HoRio, T. (1958b). J. Biocliem. Tokyo 45, 267. 



Horio, T., Higashi, T., Matsubara, H., Kusai, K., Nakai, M. & Okunuki, K. (1958). 



Biochim. biophys. Acta 29, 297. 

 Horio, T., Higashi, T., Nakai, M., Kusai, K. & Okunuki, K. (1958). Nature, Lond. 



182, 1307. 

 Keilin, D. & Hartree, E. F. (1939). Proc. roy. Soc. B127, 167. 

 Negelein, E. & Gerischer, W. (1934). Biochem. Z. 268, 1. 

 Okunuki, K. (1941). Acta Phytochim. 12, 1. 

 Okunuki, K., Sekuzu, I., Yonetani, T. & Takemori, S. (1958). J. Biochem. Tokyo 45, 



847. 

 Slater, E. C. (1949). Biochem. J. 44, 305. 

 Smith, L. (1955). Methods in Enzymology, vol. 2, p. 732. Ed. by S. P. Colowick and 



N. O. Kaplan. Academic Press, New York. 

 Smith, L. (1956). J. biol. Chem. 215, 837. 

 Yonetani, T., Takemori, S., Sekuzu, I. & Okunuki, K. (1958). Nature, Lond. 182, 1306. 



DISCUSSION 



Properties and Nomenclature of Cytochromes a and o.^ 



Morrison: I think it pertinent to point out that we have been able to obtain two spectrally 

 identical fractions on column electrophoresis of a cytochrome c oxidase preparation. 

 One of these fractions was enzymicaliy active, but the other fraction was enzymically 

 inactive. Activity could not be restored to this inactive fraction. 



Any difference in enzyme assays and chemical assays may certainly lie in the variable 

 quantity of inactive cytochrome c oxidase present. 



Morton: I think that the evidence presented by Okunuki and co-workers (this volume, 

 p. 310) is interpreted by them as establishing that there is only one cytochrome com- 

 ponent, namely cytochrome a, which is required to carry out the functions usually 

 attributed to 'cytochrome c oxidase'. However, the preparations obtained by Okunuki 

 and co-workers differ from preparations obtained by other workers, and claimed to 

 be preparations of 'cytochrome a 4- a^\ Chance, in particular, and Slater, have 

 presented evidence in support of Keilin's original identification of cytochrome a^ 

 with cytochrome c oxidase (see for example, Morton, Rev. pure appl. Chem. 8, 161, 

 1958). 



Is it possible to reconcile these conflicting views by regarding 'cytochrome a -f ^3' 

 as a single protein component with two different active sites, each involving haem a? 



