28 Philip Siekevitz 



* ptmoles DPNH or TPNH oxid./min./g. liver, 



t Act./mg. protein N. 



t Wlien resuspendedinO-12% DOC = 2-55; inO-24% DOC = 5-11; inO-33% DOC = 4-86. 



§ No. refers to length of spin at 105,000 g used to bring down pellet from DOC-treated 

 microsomes after previously spinning down RNP particles. Thus 0-2 hr. = 2 hr. pellet and 

 2-6 hr. = pellet obtained after spinning supernatant from 0-2 hr. pellet for 4 hrs. 



Data taken from Ernster, Palade and Siekevitz (unpubUshed). 



figures. However, it is clear that we are recovering a good 

 deal of the initial enzyme activity in our preparation. As 

 Table III shows, no matter what the enzyme activity of the 

 initial starting materials, the membrane pellets all had very 

 similar enzymic specific activities. Also, no matter for how 

 long we spun the diluted supernatant, the resulting pellets, 

 while difPering in amount, all had the same specific enzyme 

 activity and all looked the same in the electron micrographs. 

 All of the active enzyme which we recover is a part of a 

 structure which we can identify as the membranes of the 

 microsomes. The reduced triphosphopyridine nucleotide 

 (TPNH)-cytochrome c reductase activity behaves quite 

 differently from the DPNH enzyme in its response to 

 treatment (Table II) and in the fact that it comes down as a 

 pellet much more slowly during the centrifugation (Table III). 

 We believe that the membrane material having this activity 



