Cytochrome Oxidases of Pseudomonas Aeruginosa 



313 



example (Fig. 1), two haemin a groups may be bound to the protein in different ways, 

 one to react with oxygen, the other to transfer electrons between the first and cyto- 

 chrome c. The «3 group would be accessible to oxygen as a reactant, the a group 

 would be 'buried' or in a 'crevasse,' as in cytochrome c, and would likewise be 



■0. 



Fig. 1. A schematic diagram representing the relations of cytochrome c and 



a single oxidase protein containing one haem active in electron transfer (a) 



and one haem active in oxygen reduction (og). 



Fig. 2. 



A schematic diagram representing a possible oxygen-oxidase inter- 

 mediate of a four-haem oxidase. 



prevented from reacting with oxygen. The nature of the electron transfer mechanism 

 between a and a^ would appear to require an electron conduction band — which may 

 not exist (Taylor, Disc. Faraday Soc. 27, 237, 1959). 



The mode of reaction with oxygen might well follow that suggested for manganese 

 phthalocyanine by Orgel (see Elvidge and Lever, Proc. chem. Soc. April 1959, p. 123, 

 and June-July 1959, p. 195) in which an effective oxidation state of four would be 

 obtained in the two a^ groups (see Fig. 2). However, no spectroscopically identified 

 intermediate has been observed in the rapid reaction of cytochrome a^ and oxygen 



