Composition of Cytochrome c Oxidase 283 



pointed out that from the very beginning the two enzymes have been viewed 

 as being similar and as occurring in the same proportion wherever they were 

 found (KeiUn and Hartree, 1939). A 1:1-2 ratio has been reported by 

 Chance and Williams (1955) for the cytochromes a and a^ of rat liver 

 mitochondria. 



The two positions are defined by Slater (1958), who states that 'Those who 

 demand physical separation will not accept the separate identity of the 

 cytochromes a and a^, while those who prefer a functional differentiation 

 will treat the two cytochromes as separate identities'. 



COMPONENTS OF CYTOCHROME C OXIDASE 

 A. The Haem 



The view that cellular respiration depends on a haem was proposed by 

 Meyerhof (1924) and Harrison (1924), who believed that the experiments of 

 Warburg and his associates were conclusive enough to show that the inhibi- 

 tory action of cyanide was due to its combination with iron. Warburg (1924) 

 himself was more conservative when proposing his theory for the role of 

 iron as a biological catalyst. He simply characterized the catalyst as a com- 

 plex iron compound. When Fischer and Hilger (1924) isolated a haem from 

 yeast and higher plants the relationship between the iron and the complex 

 iron compound was established. 



The first separation of the prosthetic group of cytochrome c oxidase was 

 performed by Anson and Mirsky (1925) in Cambridge from material largely 

 supplied by Keilin. They used pyridine to extract the haems and identified 

 two haemochromes: one which corresponded to the pyridine haemochrome 

 of the haem of haemoglobin, and another with its a-band at a higher wave- 

 length. Fink (1932), subsequently, placed one of these bands at 584 m^, 

 while Negelein (1933) found two peaks in the absorption spectrum at 432 m/^ 

 and 587 m/i. More recently, Rawlinson and Hale (1949), Dannenberg and 

 Kiese (1952), Person, Wainio and Eichel (1953), and Morrison and Stotz 

 (1955) have verified that a two-banded pyridine haemochrome, whose peaks 

 are centred at 430 m/< and 587 m^<, can be prepared from mammalian heart 

 muscle or from soluble preparations of cytochrome c oxidase. 



The past and present evidence points to the nonmetallic portion of the 

 haem as being of the oxorhodo type. Rawlinson and Hale (1949) identified 

 an aldehyde rhodofying group, while Lemberg and Falk (1951) and Dannen- 

 berg and Kiese (1952) agreed that the porphyrin contains a formyl group. 

 Warburg and Gewitz (1951) found two carboxyl groups plus one presumably 

 formyl, and one vinyl group. They also withdrew their earlier suggestion 

 that the haemin might be a phytol ester. Having isolated the haemin from a 

 soluble preparation of cytochrome c oxidase, Kiese (1952) came to the con- 

 clusion that in addition to the formyl group the porphyrin contains a labile 



H.E. — VOL. I — u 



