Maturation of rabbit reticulocytes: degradation of specific reticulocyte proteins.
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Biomedical subjects
B Small
Publications and source records attributed to B Small.
Membrane proteins synthesized by rabbit reticulocytes.
Intact rabbit reticulocyte cells synthesize two predominant species of polypeptides which are components of the cell plasma membrane. Previous work (Lodish, H. F. 1973. Proc. Natl. Acad. Sci. U. S. A. 70:1526-1530.) showed that these proteins were synthesized by polyribosomes not attached to membranes. We show here that both polypeptides are confined to the cytoplasmic surface of the cell membrane. These studies utilized iodination of whole cells and of membranes with lactoperoxidase, and digestion of whole cells and membranes with chymotrypsin, One of these proteins is synthesized as a precursor, and about 20-40 amino acids are removed after it is incorporated into the membrane, We discuss the probable sites of synthesis of these and other classes of membrane proteins.
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LY339434, a GluR5 kainate receptor agonist.
The activity of a gamma-substituted glutamate analogue, (2S, 4R, 6E)-2-amino-4-carboxy-7-(2-naphthyl)hept-6-enoic acid (LY339434) and (2S,4R)-4-methylglutamic acid at ionotropic glutamate receptors has been examined. Ligand binding studies were performed using [3H] AMPA binding to membranes expressing either homomeric recombinant GluR1, GluR2, GluR4 receptors, and [3H] kainate binding to GluR5 and GluR6 kainate receptors. LY339434 and (2S,4R)-4-methylglutamic acid showed selectivity in ligand binding studies for kainate receptors over AMPA receptors. Within the kainate class of glutamate receptors, LY339434 showed selectivity for GluR5 over GluR6 whereas (2S,4R)-4-methylglutamic acid showed high affinity for both GluR5 and GluR6 kainate receptors. Examination of the functional activity of LY339434 and (2S,4R)-4-methylglutamic acid showed that both compounds evoked inward currents in dorsal root ganglion neurons (DRG) with estimated EC50 values of 0.8 +/- 0.2 microM and 0.17 +/- 0.04 microM, respectively. In GluR5 expressing HEK 293 cells, LY339434 evoked inward currents with an estimated EC50 value of 2.5 +/- 0.9 microM but had little effect on GluR6 expressing cells at concentrations less than 100 microM. LY339434 was a weak AMPA receptor agonist (EC50 values > 300 microM) as determined by activity in acutely isolated cerebellar Purkinje neurons. LY339434 and (2S,4R)-4-methylglutamic acid had agonist activity at NMDA receptors studied in cultured hippocampal neurons with EC50s of 2.5 microM and 11.7 microM, respectively. These results indicate that both LY339434 and (2S,4R)-4-methyl glutamic acid may be useful pharmacological tools for the examination of kainate receptors.
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