The reaction of Bacillus subtilis aa3-600 oxidase with oxygen: an aa3-oxidase lacking the CuA site.

The reaction of reduced cytochrome aa3-600 nm oxidase from Bacillus subtilis with oxygen has been measured. The reaction of fully reduced oxidase with oxygen was studied by the flow-flash method which employs the photosensitive CO complex to protect the enzyme from oxygen until the reaction is initiated by a photolytic flash. The rate of the reaction, measured in the Soret region, is oxygen concentration dependent at low levels of oxygen and becomes independent from oxygen above 200 microM. The reaction reaches a rate limit of 9500 s-1 at high oxygen. This type of oxygen concentration dependence indicates that the oxidation reaction is preceded by another event, probably an oxygen combination reaction. When compared to mammalian cytochrome oxidase the Bacillus oxidase exhibits a simpler reaction profile. This simpler observed reaction profile can be accounted for by the absence of CuA in the Bacillus oxidase using the same model developed for the single turnover of mammalian cytochrome oxidase.