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Membrane proteins synthesized by human reticulocytes and their precursors
Abstract:
Membrane protein synthesis in human immature erythroid cells was studied by incubating the cells with 35S-methionine in vitro. The radioactive precursor amino acid was incorporated into membrane protein in a linear fashion for approximately 60 min, after which there was only a slight increase in incorporation. Intracellular protein synthesis, in contrast, was linear for periods up to 2 h. Analysis of isolated membranes by polyacrylamide gel electrophoresis in sodium dodecyl sulphate showed that peripheral blood reticulocytes synthesized two proteins in the 4.5 region (MW=50-60000 D) and a third protein coinciding with band 6 (glyceraldehyde-3-phosphate dehydrogenase). Separation of reticulocytes into different age groups on stractan II gradients showed more immature reticulocytes synthesize a wider range of membrane proteins, extending from bands 4.1 to 8. When nucleated red cells were present in the incubations, synthesis of band 3 was also observed. Earlier erythroid precursor present in erythropoietic BFU-E cultures synthesized spectrin in addition to the other membrane proteins. The data indicate that human red cell membrane protein synthesis follows a programmed pattern and that as the erythroid elements mature they lose the capacity to synthesize certain membrane proteins.
Insights
Human red blood cell membrane protein synthesis follows a programmed pattern. Immature erythroid cells synthesize a wider range of proteins, losing this capacity as they mature.
Area of Science:
- Cell Biology
- Hematology
- Biochemistry
Background:
- Erythropoiesis involves the maturation of erythroid cells.
- Membrane proteins are crucial for red blood cell function.
- Understanding protein synthesis during erythropoiesis is key to hematological research.
Purpose of the Study:
- To investigate the pattern of membrane protein synthesis during human erythroid cell maturation.
- To identify specific membrane proteins synthesized at different erythroid developmental stages.
Main Methods:
- Incubation of human immature erythroid cells with 35S-methionine in vitro.
- Analysis of membrane proteins using polyacrylamide gel electrophoresis in sodium dodecyl sulphate.
- Separation of reticulocytes by age using stractan II gradients.
Main Results:
- Membrane protein synthesis was linear for ~60 min, while intracellular synthesis continued for up to 2 h.
- Reticulocytes synthesized proteins in the 4.5 region and band 6 (glyceraldehyde-3-phosphate dehydrogenase).
- Immature reticulocytes synthesized a broader range of membrane proteins (bands 4.1-8), with band 3 synthesis observed in nucleated red cells and spectrin in earlier precursors.
Conclusions:
- Human red cell membrane protein synthesis is a programmed process.
- Erythroid cell maturation is associated with a loss of capacity to synthesize specific membrane proteins.
- This study elucidates the developmental regulation of membrane protein expression in erythroid cells.