Cytochrome Oxidases of Pseudomonas Aeruginosa 



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reduction by /j-phenylenediamine occurs even under aerobic condition, though 

 the reduction rate is slow compared with the case under anaerobic conditions. 

 The difference in rate between the two conditions indicates that cytochrome 

 a itself is so slightly autoxidizable that this autoxidation cannot be considered 

 to result from an enzymic activity. At present, it is not known whether the 



Fig. 1 . Effect of cytochrome c on the oxidation of cytochrome a. Cytochrome a 

 was incubated with /7-phenylenediamine aerobically in 'Aerobe' and anaerobically 

 in 'Anaerobe'. Other additions were made aerobically in both cases. The arrows 

 indicate time of addition of each reagent: a, 10~* m /j-phenylenediamine and a 

 trace of sodium borohydride; b, 5 x 10^* M oxidized cytochrome c; c, a trace 

 of sodium dithionite. The addition of borohydride was made to prevent 

 autoxidation of/7-phenylenediamine. 



autoxidizability results from the property of cytochrome a itself or from 

 that of its modified form, just like the case of native and modified cytochrome 

 c. If cytochrome c is present, the reduction of cytochrome a by /j-phenylene- 

 diamine rapidly occurs under anaerobic condition. On the other hand, when 

 cytochrome c is aerobically added to the cytochrome a previously reduced by 

 an excess amount of /?-phenylenediamine, cytochrome a cannot maintain its 

 reduced form, and a rapid oxidation immediately occurs. This phenomenon 

 of cytochrome a corresponds to that of the cytochrome oxidase activity of the 

 purified cytochrome a preparation, as well as to that of the particulate 

 preparation. It is, therefore, considered that cytochrome a itself displays 

 an essential role in the cytochrome oxidase activity of its purified preparation. 

 This consideration induces a concept in which the system, 'cytochrome c plus 

 cytochrome a' works as cytochrome oxidase (so-called cytochrome a^^. 

 The physicochemical constants of P-cytochrome oxidase are given in 



