Studies on the synthesis of serum albumin by ribonucleoprotein particles isolated from rat liver.

One of the objectives of the work in this Laboratory on the synthesis of serum albumin has been to determine the simplest morphological structure that can synthesize a specific protein. This should help our understanding of the mechanism of protein synthesis and should provide evidence of the role of the various morphological constituents of the cell in the biosynthesis of protein. Experiments suggesting that the isolated microsome fraction from rat liver can synthesize serum albumin have been reported by Campbell, Greengard & Kernot (1960); Campbell & Kernot (1962). Ribonucleoprotein particles, isolated from the microsome fraction by removing the membrane component with various detergents, incorporate amino acid into protein (Komer, 1959, 1961a; Rendi & Hultin, 1960; Takanami, 1960; Kirsch, Siekevitz & Palade, 1960). This suggested that the synthesis of serum albumin could be studied in isolated particles. Korner (1960, 1961b) reported that 14C-labelled amino acids on incubation were incorporatedintoserumalbuminbyisolatedparticles after treatment of the microsomal fraction with deoxycholate. The ribonucleoprotein particles used in the metabolic experiments described below were prepared by the method of Rendi & Hultin (1960). This method provides particles with high activity for the incorporation of amino acids. There is evidence that these particles which are prepared with deoxycholate, Lubrol and a concentrated solution of potassium chloride are almost completely free of other constituents of the cytoplasm (Decken, 1961). In albumin synthesis ribonucleoprotein particles differ in an important respect from the particles of the microsome fraction: the amount of serum albumin associated with the ribonucleoprotein particles is very small. Nevertheless, it seemed worth while to investigate the problem of albumin synthesis in such particles with the methods previously described for microsomes. Some aspects of this work have been reported by Decken & Campbell (1961 a). * Present address: Wenner-Gren Institute for Experimental Biology, Stockholm, Sweden.