THE SYNTHESIS OF HEMOGLOBIN IN A CELL-FREE SYSTEM

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Abstract
The incorporation of Cl4-labeled amino acids into protein in a system containing microsomal particles from rabbit reticulocytes plus soluble enzymes is described. Preliminary results indicate that the process under investigation is the synthesis of soluble cell protein which consists mainly of hemoglobin. Evidence leading to this conclusion may be summarized as follows. Incorporation of labeled amino acid was stimulated by addition of a complete mixture of amino acids of a particular composition. Soluble proteins containing radioactivity were formed, and radioactive hemoglobin was isolated. Leucine, isoleucine, and valine were incorporated in the ratios in which they are present in crude hemoglobin. The results also provide evidence that the amino acid sequence of the final protein, hemoglobin, is determined in the microsomal particle because although the pH 5 enzyme of guinea-pig liver forms leucine-RNA and isoleucine-RNA at similar rates, these amino acids are incorporated into protein only in the proportions in which they exist in hemoglobin.