90 



SUBCELLULAR PARTICLES 



Fig. 7. Diagrammatic representation of the sub- 

 units of the mitochondrion. 



logically intact shows only a very restricted number of enzymatic activities. It 

 does not oxidize citrate or isocitrate; it does not reduce externally added cyto- 

 chrome c or DPN; and it does not oxidize DPNH. Only when the mitochondrion 

 is damaged morphologically do these activities emerge (33). This is the well 

 known opening phenomenon which underlies some basic features of mitochon- 

 drial structure. The neglect of this phenomenon has led Hogeboom and Schnei- 

 der (21, 30) to their conclusion, which has had wide currency among biochemists, 

 that the mitochondrion does not carry out the complete citric acid cycle and that 

 some of the key enzymes of the cycle are localized outside the mitochondrion. 

 It has taken almost 10 years to correct this erroneous conclusion, and it will 

 probably take many more years to clear up the confusion which has been created. 

 In our laboratory we have taken the approach that an understanding of elec- 

 tron transport is the key to oxidative phosphorylation and, in turn, that an under- 

 standing of oxidative phosphorylation is the key to mitochondrial structure and 

 function. Our main efforts, therefore, have been concentrated on the chemical 

 structure and components of the electron transfer chain as a necessary preliminary 

 to an attack on oxidative phosphorylation. The point of departure for these 

 studies has been the electron transfer particle which according to our evidence is 

 the sniallest common denominator of the complete electron transfer process; i.e., 

 the transfer of electrons from a substrate to molecular oxygen. 



