26o DANIEL M. ZIEGLER 



CoQ (Fig, 3). These data again demonstrate that the succinic-CoQ 

 reductase contains a component other than the haem group that can 

 function as an electron carrier between the flavoprotein and CoQ. Since 

 non-haem iron is the only other known compound present in the enzyme 

 that undergoes oxidation and reduction it is probable that the iron is 

 responsible for the 415 m/x band observed in the reduced enzyme. 



References 



1. Green, D. E., Ziegler, D. M., and Doeg, K. A., Arch. Biochem. Biophys. 85, 



280 (1959). 



2. Doeg, K. A., Krueger, S., and Ziegler, D. M., Biochim. biophys. Acta 41, 492 

 (i960). 



3. Pumphrey, A. M., and Redfearn, E. R., Biochem. jf. 72, 2P (1959). 



4. Singer, T. P., Kearney, E. B., and Bernath, P., J. biol. Chem. 223, 599 (1956). 



5. Ziegler, D. M., and Doeg, K. A., Biochem. biophys. Res. Comm. I, 344 (1959). 



6. Crane, F. L., Glenn, J., and Green, D. E., Biochim. biophys. Acta 22, 475 

 (1956). 



7. Beinert, H., and Sands, R. H., Biochem. biophys. Res. Comm. 3, 41 (i960). 



8. Massey, V., Biochim. biophys. Acta 30, 508 (1958). 



9. Green, D. E., and Burkhard, R. K., Arch. Biochem. Biophys. (in press). 



10. Hatefi, Y., Haavik, A. G., and Jurtshuk, P., Biochem. biop/iys. Res. Comm. 3, 



281 (i960). 



11. Linnane, A., and Ziegler, D. M., Biochim. biophys. Acta 29, 630 (1958). 



12. Ziegler, D. M., and Doeg, K. A. (manuscript in preparation). 



13. Fluharty, A. L., and Sanadi, D. R., Fed. Proc. 19, 608 (i960). 



14. Conover, T. E., and Ernster, L., Acta chem. scand. (in press). 



Discussion 



Redfearn : This hypothesis raises the problem of the transfer of the electrons 

 from flavoprotein which carries two electrons through a one electron carrying 

 system (the iron) then again to a two-electron carrier. It was nice to think that the 

 quinone could function as a semi-quinone and thus mediate the reaction between 

 two-electron carriers and the one electron carrying cytochromes. Secondly, I 

 noticed that you used Q., in your assay system. According to Crane's results on 

 acetone-extracted preparations Q., prodviced an antimycin-insensitive pathway, 

 which suggests that the site of action of Qo was not the same as that of the naturally 

 occurring Qio- Would you care to comment on this ? 



Ziegler : Is it necessary to assume that the flavoprotein is fully reduced during 

 active electron transport ? I would be more inclined to believe that in the intact 

 succinoxidase particle the flavoprotein may be reduced only to the semiquinoid 

 form, and if this is the case you would have one electron transfer during the 

 oxidation of succinate. 



With reference to the last point you raised, the reoxidation of reduced Q2 is 

 partly antimycin-insensitive and as you increase the length of the side chain you 

 induce full antimycin sensitivity. However, in the reduction of Q the succinic-Q- 

 reductase will react rapidly with either Qio or homologues of Q and we have used 



