The role of serum albumin as a precursor of the soluble tissue proteins and the serum globulins of the rat bearing liver tumours

Abstract

A rat with liver tumors induced by feeding 4-dimethylaminoazobenzene was intravenously injected with a solution containing (Cl4) alanine-and (C14) lysine-labeled rat-serum albumin and killed 90 minutes after the injection. The liver, liver tumor, kidney and spleen were homogenized and soluble extracts of the tissues were obtained. Samples of these were treated with trichloroacetic acid and the radioactivity of the lysine and alanine in hydrolysates of the precipitated proteins lysine and of free alanine and in the supernatants were determined. The amount of serum albumin in the tissue extracts was determined by means of an antiserum. Total albumin in the extracts greatly exceeded that estimated as due to the presence of blood. The plasma proteins obtained from the rat at death were fractionated by zone electrophoresis into albumin plus a-globulin, B-globulin and gamma-globulin, and the radioactivity of the alanine and lysine in the hydrolysates of each fraction was determined. From the ratio of the radioactivity of the free amino acids in the tissues to that of the amino acids in the tissue proteins it is concluded that there is no evidence that serum albumin is utilized for the synthesis of soluble tissue proteins without first being broken down to free amino acids. In this respect liver tumor did not appear to differ from the other tissues studied. No evidence could be found for the interconversion of serum albumin and serum globulin at other than an amino acid level.