314 Discussion 



(see for example, Chance, in Conference on Oxidative Metal Enzymes, Tokyo, 1957). 

 Also, this configuration would necessitate a conduction band, as in Fig. 1 . 



The configurations described above appear to off"er no better agreement with 

 available experimental data than a sequence in which the cytochromes interact by 

 collision (Chance and Williams, Advanc. Enzymol. 17, 65, 1956) and in which the 

 chain is represented as a dimer in order to avoid the necessity of a two-to-one change 

 in electron transfer from flavoprotein to cytochrome (Chance and Williams, Advanc, 

 Enzymol. 17, 65, 1956; Slater, Spallanzani Meeting, 1959). Two forms of the chain 



substrate — ^ f p 



subs,ro,e -^ fp -^ (^) -^ Q ^ Q -^ Q ^ (^) -. o. 



Fig. 3. Dimerized respiratory chains (a) with two proteins. 



appear in Fig. 3, one in which the components are dimerized and one in which two 

 parallel chains are operative. 

 Smith: In the presence of cholate where the reactions of cytochromes 03, a and c are 

 slower, there can be seen a diff"erence in the kinetics of changes in the absorption 

 spectrum at 445 and 605 mfi, indicating that these are not two absorption bands of 

 one compound. This would agree with Chance's observations of a difference in rate 

 of change of the two bands on addition of oxygen to anaerobic preparations. 



The Prosthetic Groups of Pseudonionas Cytochrome Oxidase 



By T. HoRio AND M. D. Kamen (Waltham) 



HoRio: Very recently, Kamen and I tried a stepwise reduction of Pseiidomonas cytochrome 

 oxidase by titration of sodium ascorbate which was one of its substrates. 



As shown in the accompanying figure, the a2-type haem (630-625 m/0 was much 

 more slowly reduced than c-type haem (549 m/< and 554 m//). The shoulder around 

 450 m/< was influenced by both reductions of 02-type haem and c-type haem, because 

 the flo-type haem split from the protein moiety by acid-acetone showed another peak 

 in that region. In view of this result, a2-type haem could be lower in oxidation- 

 reduction potential than c-type haem. A rough calculation based upon their equi- 

 librium shows that the difference between the normal redox-potentials of the two 

 haems might be 20-30 mV. In a previous report (Horio, Higashi, Matsubara, Kusai, 

 Nakai and Okunuki, Biochim. biophys. Acta, 29, 297, 1958), the double a-absorption 

 peaks at 549 m/< and at 554 m/< of P-cytochrome oxidase had been supposed to be 

 caused by two different kinds of c-type haems. But the lack of difference in the step- 

 wise reduction of the oxidase at 549 m/< and 554 m/t indicated that these double peaks 

 resulted from the same c-type haem. The iron analysis of the oxidase mentioned in 

 the paper doubtlessly shows that P-cytochrome oxidase contains one a-type haem and 

 one c-type haem in each molecule. This finding might be useful for an attack on the 

 reaction mechanism of a cytochrome oxidase. 



