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Transferrin and the transferrin cycle in Belgrade rat reticulocytes
M D Garrick1, K Gniecko, Y Liu
1Department of Biochemistry, State University of New York, Buffalo 14214.
The Journal of Biological Chemistry
|July 15, 1993
Summary
Belgrade rats have a genetic anemia due to ineffective iron utilization. Their reticulocytes fail to retain iron properly after uptake, causing hypochromia and microcytosis.
Area of Science:
- Hematology
- Genetics
- Cell Biology
Background:
- Belgrade rats exhibit an autosomal recessive anemia characterized by hypochromia and microcytosis.
- Iron uptake into reticulocytes is significantly reduced, though transferrin uptake remains normal.
Purpose of the Study:
- To precisely locate the defect in the transferrin cycle responsible for Belgrade rat anemia.
- To compare the transferrin cycle kinetics in Belgrade versus normal rat reticulocytes.
Main Methods:
- Systematic comparison of the transferrin cycle in Belgrade and normal reticulocytes.
- Functional assays of purified Belgrade transferrin and receptor binding.
- Kinetic analysis of transferrin endocytosis, exocytosis, and iron retention.
Main Results:
- Belgrade reticulocytes have normal transferrin function and receptor affinity but twice the number of receptors.
- Endocytosis and exocytosis rates are altered, yet overall transferrin cycle time is unchanged.
- Belgrade reticulocytes retain only half the iron taken up, with ineffective iron unloading from vesicles.
Conclusions:
- The defect in Belgrade rats lies in ineffective iron utilization within or near endosomes.
- This leads to significant iron loss and accounts for the observed anemia, hypochromia, and microcytosis.