26 Philip Siekevitz 



microsomes could be dismantled with 0-3 per cent deoxy- 

 cholate (DOC) so as to render "soluble" their reduced di- 

 phosphopyridine nucleotide (DPNH)-cytochrome c reductase 

 activity. What is meant by this was that if the disintegrated 

 microsomal suspension were spun down for two hours at 

 105,000 g to bring down the ribonucleoprotein particles, this 

 enzyme remained in the supernatant solution. What Ernster 

 did was to take this supernatant fraction which contained all 

 of the microsomal enzyme, albeit somewhat inactivated, and 

 effectively get rid of the DOC by diluting the supernatant 

 solution some five- to ten-fold with a sucrose solution. As a 

 control he had one specimen to which was added the same 

 amount of sucrose solution but containing the same concen- 

 tration of DOC as was used originally to disintegrate the 

 microsomes. After spinning at 105,000 g for two, or six, or 

 sixteen hours, he found that he obtained a large pellet from 

 the sucrose-diluted supernatant but only a very small pellet 

 from the sucrose and DOC-diluted supernatant. Palade took 

 a picture of this pellet from the sucrose-diluted supernatant 

 and, as Fig. 11 shows, found that a specimen of microsomal 

 membranes had been obtained, minus their formerly attached 

 nucleoprotein particles, but which was disorganized in that 

 only a few typical microsomal vesicles could be seen. At 

 present we take the view that the membranes were initially 

 truly solubilized, perhaps by being spread out in a thin film in 

 the presence of the detergent, and by lowering the concentra- 

 tion of the detergent, they recoiled upon themselves but not in 

 their original configuration, and became responsive to being 

 sedimented. Tables II and III give some representative 

 data on the properties of this microsomal enzyme and on the 

 enzyme of the microsomal membrane fraction. With regard 

 to the variations in response of the microsomal DPNH- 

 cytochrome c reductase to treatment: briefly, sometimes we 

 obtained microsomes with high enzymic activity, and if let 

 stand in sucrose alone, or more so in sucrose-DOC solution, 

 they lost much of their activity. Sometimes, the original 

 microsomes had low activity, but could be activated by stand- 



