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Protein Synthesis in the Maturing Reticulocyte

Journal of Biological Chemistry, ISSN: 0021-9258, Vol: 242, Issue: 7, Page: 1533-1540
1967
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Metrics Details

  • Citations
    17
    • Citation Indexes
      17
      • CrossRef
        17
  • Captures
    1

Article Description

In order to determine why protein synthesis declines with reticulocyte maturation, rabbit reticulocytes separated by age on a density gradient of bovine serum albumin were studied. The ribosomal fraction was identified as the cell fraction largely responsible for this decline. Magnesium ion concentration in the soluble fraction of the cell declines with maturation. This decline may have functional significance, since the cell-free system from old cells showed a greater dependence on added magnesium than did the cell-free system from young cells. In response to added polyuridylic acid, the cell-free system from old cells synthesized polyphenylalanine at a slower rate than did the cell-free system from young cells, even when tested with equal concentrations of ribosomes. This difference was attributed to decreased responsiveness of the ribosomes from old cells to polyuridylic acid. A similar difference in responsiveness to endogenous messenger for hemoglobin would fully account for the observed difference in hemoglobin synthesis. A reticulocyte ribonuclease activity, extracted from the intact cells with a hypertonic solution containing ethylenediaminetetraacetate and tris(hydroxymethyl)aminomethane, declines with maturation from the earliest stage studied onward. The difference in activity of young and old cells was not due to a difference in membrane permeability, a deficiency in amino acids or adenosine triphosphate, nor to a diffusable activator or inhibitor of protein synthesis. No difference was found in the effects of heme, protoporphyrin IX, iron, or high and low oxygen tensions in either whole cells or cell fractions, nor in the ribosomal ribonucleic acid to protein ratio.

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