CYTOCHROME OXIDASE COMPONENTS 



By M. Morrison and E. Stotz 



Department of Biochemistry, School of Medicine and Dentistry, 

 University of Rochester, Rochester, New York 



THE PROSTHETIC GROUP OF CYTOCHROME OXIDASE 



Two of the major unsolved problems in the area of electron transport are: 



(1) the mechanism by which the electrons are passed on to reduce oxygen and 



(2) the chemical mechanism by which energy is captured in biological oxida- 

 tion and transformed into a utilizable chemical form. 



An understanding of the structure of the prosthetic group of the enzyme 

 which catalyzes the reduction of oxygen is of prime importance to the first of 

 these problems. Extensive work by many investigators (see, for example, 

 Dannenberg and Kiese, 1952; Kiese and Kurz, 1954; Lemberg, 1953; 

 Lemberg, Bloomfield, Caiger and Lockwood, 1955; Morrison and Stotz, 

 1955; Person, Wainio and Eichel, 1953; Warburg, Gewitz and Volker, 1955) 

 has clearly established that the prosthetic group of this enzyme is an iron 

 porphyrin compound which has been labelled 'haemin a" or 'cytohaemin'. 



One of the problems of estabhshing the structure of the prosthetic group 

 of cytochromes a has been in obtaining adequate quantities of the haemin free 

 of contaminating lipids and other haemins. In the course of developing 

 procedures designed to obtain pure haemin a, several interesting observations 

 were made. 



A study of the haemins present in a cytochrome oxidase preparation showed 

 that both haemin a and cryptohaemin a were extracted from the preparation 

 (Morrison and Stotz, 1955). Investigation (Morrison, Connelly and Stotz, 

 1958) of the rate of extraction of haemins from a cytochrome oxidase prepara- 

 tion indicated that cryptohaemin a and protohaemin are extracted more 

 rapidly than haemin a. More recently, the slower extraction rate of haemin a 

 was again demonstrated, using liver mitochondria as a starting material. 

 This differential rate of extraction suggested that cryptohaemin a was not an 

 artifact derived from haemin a by the extraction and isolation procedures, as 

 other workers have implied. This was further strengthened by studies which 

 indicated that haemin a and cryptohaemin a were not interconvertible by any 

 treatment employed in the extraction or subsequent manipulation of the 

 haemins. 



Thus, cryptohaemin a would appear to be present in the starting haemo- 

 protein preparation, bound to protein. The spectral properties of haemin a 



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