Abstract
Summary
To learn where ferritin is synthesized—on free and/or membrane-bound (poly)ribosomes—fractions rich in (poly)ribosomes were isolated from rat livers by the method of Blobel and Potter (5), with modifications. The degree of separation of membrane-bound (poly)ribosomes from free (poly)ribosomes was checked by electron microscopy, biochemically, and with a radioactive tracer. Results of experiments on the incorporation of labeled amino acids into the protein of ferritin (apoferritin) indicate that both, membrane-bound (poly)ribosomes and free (poly)ribosomes are implicated in the synthesis of apoferritin, and that free (poly)ribosomes synthesize substantially more apoferritin per milligram RNA than bound (poly) ribosomes.
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