232 Paulette Chaix 



than in the first. We do not have any experimental evidence to support any 

 of the very numerous hypotheses which may be advanced to explain the 

 different behaviour of the two types of cell. 



3. Our attempts at fractionation of yeast in the exponential phase of 

 aerobic and anaerobic growth have allowed us to establish several important 

 points. We have been able to devise an isolation technique for mitochondria 

 of aerobic and anaerobic yeast, using a polyvinylpyrrolidone medium, which 

 allows us to obtain them in a good state of integrity as shown by electron- 

 microscope examination. The aerobic mitochondria isolated in this medium 

 have a spectrum in which the ca band has the same intensity as that observed 

 in the spectrum of intact cells. These experiments speak strongly against 

 the existence of an extra-mitochondrial cytochrome c. 



The anaerobic mitochondria are much smaller than the aerobic ones but 

 more dense, since they sediment largely at 4000 x g. The haematin com- 

 ponents characterized by a-bands at 552-5 and 558 m^^ and /3-bands at 

 525 and 532-5 m/i, not appearing until after reduction by dithionite, appear 

 to belong not to these anaerobic mitochondria but rather to homogeneous 

 granules which sediment mainly between 4000 and 25,000 X g. Our evidence 

 does not appear to permit the assignment of lactate dehydrogenase activity to 

 these haematin components. 



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