ZONAL CENTRIFUGATION OF MICROSOMES FROM RAT LIVER - RESOLUTION OF ROUGH- AND SMOOTH-SURFACED MEMBRANES

The microsomal fraction of rat liver consists of free ribosomes and smooth- and rough-surfaced vesicles that are derived from fragmentation of the endoplasmic reticulum (1). Two methods, based on differences in density and sedimentation rate, have been used to subfractionate microsomes from rat liver into predominantly smooth- and rough-surfaced fractions (2,3). However, both methods have been hampered by the small capacities of commercially available high-speed centrifuge rotors, difficulties in maintaining gradient stability during acceleration and deceleration, and problems in loading the gradient and the sample. The development of the zonal ultracentrifuge system (4) has largely overcome these difficulties. This communication reports our results on the separation of different elements of the microsomal fraction in a B-XXIX zonal rotor. © 1969.