Characterization of specificity of incorporation of 75Seselenomethionine into human apoproteins following in-vivo injection of the radioactive amino acid precursor is reported. Apoprotein fractionation was attained by serial ultracentrifugation, anhydrous partial delipidization, decyl sulfate solubilization with Sephadex G-150 gel filtration into polypeptide fractions, Sf-I, and Sf-II, for VLDL, and LDL subfractions. Similarity of the Sf-I fractions isolated from VLDL, LDL1 and LDL2 was defined by gel exclusion volume, disk-gel electrophoresis, immunodiffusion, and amino acid composition. Enrichment of the Sf-I fractions with75Se-SM in VLDL and LDL subfractions was observed, suggesting a possible use for this isotopic method for the investigation of apoprotein metabolism.

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