Fractionation of proteins of the microsomes of rat liver by means of a non-ionic detergent

Abstract

The microsome fraction from rat liver was treated with the non-ionic detergent Lubrol W, which solubilized approximately one-half of the protein, 60-80% of the lipid phosphorus and a negligible amount of ribonucleic acid. When rats were killed 2 minutes after the injection of (Cl4) phenylalanine a higher specific radioactivity was found in the protein of the Lubrol pellet than of the supernatant liquid. Six minutes or longer after injection the specific radioactivity of the Lubrol super-natent liquid was more than twice that of the protein of the pellet. Treatment of the Lubrol pellet with either sodium perfluoro-octanoate or sodium deoxycholate released proteins which, 2 minutes after injection, possessed a low specific radioactivity. The pellets so obtained had a higher specific radioactivity than almost all other microsomal protein fractions examined. The proteins of the Lubrol supernatant liquid were separated into 4 fractions, differences in solubility in strong solutions of magnesium sulfate, ammonium sulfate and water being utilized. The specific radioactivities of these fractions showed the same pattern of distribution, whatever the time interval after the injection of (C14) phenylalanine. The final fraction containing these proteins least readily precipitated became labeled very quickly; 2 minutes after injection it had a specific radioactivity as high as that of the proteins of the sodium perfluoro-octanoate pellet. The present results indicate that a number of microsomal proteins which can easily be solubilized become labeled simultaneously.