298 



W. W. Wainio 



cyanide is inhibiting the transfer of two electrons, whereas the other (dots) is 

 drawn on the assumption that each cyanide is inhibiting the transfer of one 

 electron. In this experiment the values fit the theoretical indicating that each 

 cyanide is inliibiting the transfer of two electrons, but in other experiments the 

 fit has not been as good, so that the points have fallen between the two curves. 



-SO 



-50 



-10 -9 -8 -7 -6 -5 --^ -J 



Lo<^ M Cone. NaCN 



Fig. 6. Effect of cyanide on the activity of cytochrome c oxidase. curve 



based on the assumption that each cyanide is forming a complex with a site 



transferring two electrons; .... curve based on the assumption that each cyanide 



is forming a complex with a site transferring one electron. 



Therefore it can only be concluded that there are two binding sites for cyanide 

 in a cytochrome c — cytochrome c oxidase mixture and that each site may 

 control the transfer of two electrons each. Since this inflected curve is obtained 

 on incubation with the cyanide only when the oxidase and the cytochrome c 

 are together, it cannot yet be concluded that the two cyanide-sensitive sites 

 are the two copper atoms. However, more than a single site must be involved 

 and it must be borne in mind that copper will react with cyanide. 



SUMMARY 



The proposition has been explored that cytochrome c oxidase is one 



enzyme constituted of haem, copper, lipid and protein. It is suggested that the 



spectral and reaction anomalies which have supported the existence of two 



components, namely, cytochrome a and cytochrome a^, be reconsidered in 



