224 Discussion 



out oxidative phosphorylation, as has been shown by several workers. In our labor- 

 atory, Miss Hovenkamp has been continuing the studies, begun by Tissidres and 

 myself in Cambridge, of the system bringing about oxidative phosphorylation in 

 particles isolated from Azotobacter. The P:0 ratios are low compared with those 

 found with isolated mitochondria from animal cells, but the rate of respiration is so 

 high that the rate of synthesis of ATP/mg protein by these bacterial-membrane 

 fragments is the highest ever recorded. 



Miss Hovenkamp has recently succeeded in dissociating reversibly the phosphoryl- 

 ation from the respiratory chain by suspending the particles in a medium of low ionic 

 strength, following by centrifugation at high speed. Particles obtained in this way 

 oxidize DPNH with little phosphorylation. Oxidative phosphorylation can be re- 

 constituted by incubation of these particles with Mg++ and the supernatant obtained 

 in this centrifugation {Nature, Lond. 184, 471, 1959). It should be noted that, unlike 

 other supernatant factors, Miss Hovenkamp's is derived not from the cell sap but 

 apparently by disintegration of the washed small particles themselves. We do not yet 

 know whether this supernatant factor is an enzyme related to oxidative phosphoryl- 

 ation, or is perhaps a structural factor required to restore the structure of the particles 

 which has been disturbed by incubation in media of low ionic strength. This question 

 is now being studied by Hovenkamp in Pinchot's laboratory. 



