Labeling With 14c Amino Acids of Albumin-Like Protein by Rat Liver Ribonucleoprotein Particles

Abstract

Ribonucleoprotein particles were prepared by treatment of rat liver microsomes with detergents and high concentrations of KCI. They were active in incorporating 14C amino acids into protein when incubated with cell sap together with ATP, GTP, and a system to regenerate the triphosphates. The albumin of the incubation mixture, soluble at I05,000 g, and that of the fraction released by ultrasonication of the particles were studied by immunoclectrophoresis in agar gel. When the ribonucleoprotein particles were incubated with cell sap the immunological precipitation lines formed with antiserum to rat serum albumin were highly radioactive as tested by autoradiography. After zone electrophorcsis on cellulose acetate, two immunologically reactive albumins were obtained which differed in their electrophoretic mobility from rat serum albumin. Labeled albumin, when purified on DEAE-cellulose columns, retained its radioactivity as tested by autoradiography following immunoelcctrophoresis. On cellulose acetate this purified albumin showed an electrophoretic mobility higher than that of rat serum albumin.

The Kinetics in vivo of the Synthesis of Albumin‐Like Protein and Albumin in Rats

“…This is due to the presence in these tissues of a protein similar to albumin [6,7,9,10]. When applying appropriate purification procedures, Judah and Nicholls observed that liver slices continued to incorporate ['4C]leucine into albumin after incorporation into total protein had been interrupted by cycloheximide or excess unlabelled leucine [Ill.…”

“…In contrast to the easy isolation from serum, rather extensive purification is required to obtain pure albumin from biological material involved in albumin synthesis, such as liver [l-41, hepatoma [2,3], hepatocyte suspensions [ 5 ] , and cell-free proteinsynthesizing systems from liver [6-81. This is due to the presence in these tissues of a protein similar to albumin [6,7,9,10]. When applying appropriate purification procedures, Judah and Nicholls observed that liver slices continued to incorporate ['4C]leucine into albumin after incorporation into total protein had been interrupted by cycloheximide or excess unlabelled leucine [Ill.…”