Abstract
1. 1. Injection into rabbits of mitochondria, microsomes or “cell sap”, isolated from homogenates of rat liver, leads to the formation of antibodies against the antigens characterizing these different fractions. By means of agar diffusion techniques it can be demonstrated that the antigenic composition of these fractions shows considerable differences. Proteins of characteristic antigenic specificities can be found exclusively in each of the fractions. In addition, both the membranous fraction and the nucleoprotein fraction of the microsomes can be characterized immunologically. In this paper the nature of the immunological differences between the different cellular structures is described and some of the factors influencing the distribution of the antigens are discussed. 2. 2. The cellular antigens characterizing the liver homogenates are both chemically and immunologically distinct from the serum proteins. However, as can be shown by means of double diffusion experiments in agar and by means of immunophoresis, injection of the liver microsomes into the rabbit leads to a strong production of antibodies against both serum albumin and a number of serum globulins. These antibodies are not obtained when isolated mitochondria or the cell sap are used for the production of the antisera. The significance of these findings is briefly discussed. 3. 3. When liver slices are incubated with radioactive amino acids and the slices subsequently fractionated and tested immunologically, the incorporation of isotopes into the different antigens can be recorded by means of autoradiography of the agar plates. Incorporation into distinct and immunologically normal cellular proteins is also obtained when cell free systems (cell sap + microsomes + ATP generating system) are used to provide the antigen solutions. In both cases, antigens are found which, under the experimental conditions applied, have a higher specific activity when extracted from the microsomes than when isolated from the cell sap. The bearing of this and similar findings on problems relating to the biosynthesis of proteins is discussed.
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