[3H]ouabain binding and 86rubidium uptake during the cell growth cycle in L5178Y murine lymphoblasts

There was a parallel alteration in [³H]ouabain binding and ⁸⁶Rb⁺ uptake during the cell growth cycle in L5178Y murine lymphoblasts. The initial rate of Rb⁺ uptake and [³H]ouabain binding was highest at the stationary phase of the cell growth cycle. The possible relationship between changes in cation transport and membrane properties to the cell growth cycle is discussed.     

Peripheral dopamine receptor identification: Properties of a specific dopamine receptor in the rat adrenal zona glomerulosa

Specific dopaminergic receptors were found in the rat adrenal zona glomerulosa. Specific binding as defined by the difference in [³H]-spiroperidol binding in the presence or absence of excess dopamine was saturable and of high affinity. Stereospecificity of binding to the dopaminergic receptor was demonstrated by the fact that (+)-butaclamol was 300-fold more active at displacing [³H]-spiroperidol from the binding site than (?)-butaclamol. A Scatchard analysis of the data revealed a K_D = 6.9 nM and a B_max = 173 pmol/gm for the binding of [³H]-spiroperidol to adrenal capsular homogenate binding site. Characteristics of this receptor place it in the recently defined D2 dopamine receptor subclass.     

Surface biochemical changes accompanying primary infection with Rous sarcoma virus. I. Electrokinetic properties of cells and cell surface glycoprotein:glycosyl transferase activities

A special class of polysomes synthesizing tubulin was determined using embryos of the sea urchin, Hemicentrotus pulcherrimus. Three criteria were established for identification of polysomes carrying nascent tubulin, i.e., nascent tubulin on polysomes should have (i) colchicine binding activity, (ii) precipitability with vinblastine and (iii) coincidence in mobility by electrophoresis with tubulin. Two classes of polysomes had polypeptides which accorded with the three criteria. One was tetramers and the other was composed of 15–20 ribosomes. From data reported previously on the molecular weight and amino acid composition of completed microtubule proteins, it was suggested that the class of polysomes composed of 15–20 ribosomes constituted the polysome-synthesizing tubulin of sea urchin embryos. The nature of the nascent polypeptides carried by the tetramer polysomes having colchicine binding activity and precipitability with vinblastine could not be clarified.     

Platelet adhesiveness and aggregation: the collagen:glycosyl, polypeptide:N-acetylgalactosaminyl and glycoprotein:galactosyl transferases of human platelets

Four glycoprotein:glycosyl transferases were identified, purified, and characterized from human platelets. The enzymes present were collagen:glc, collagen:gal, polypeptide:galNAc, and glycoprotein:gal; the fetuin:glcNAc transferase was absent. Each of the 4 transferases was found to be almost exclusively bound to the platelet plasma membrane. Incubation of platelet homogenates without exogenous acceptors yielded no transfer of monosaccharide, indicating the complete lack of endogenous acceptors. These results lead to the interesting speculation that the transferases may not be responsible in the mature platelet for glycoprotein synthesis at all, but rather that they may function for intercellular adhesion and the primary step in hemostasis, the adhesion of collagen to platelets.     

Synthesis of glycoprotein, glycolipid, protein, and lipid in synchronized L5178Y cells

Synthesis of four macromolecular classes found in membranes—glycoprotein, glycolipid, protein, and lipid—was measured as a function of time of the cell cycle in synchronized L5178Y cells. Incorporation of leucine, choline, fucose, glucosamine, or thymidine into the cells, protein, nucleic acid, or lipid was measured by pulse-labeling for ½ hr at ½ hr intervals after release from the mitotic block. The amount of protein, lipid, glycoprotein, or glycolipid released or secreted into the medium by the L5178Y cells was also measured as a function of time of the cell cycle. Cellular protein was found to be synthesized throughout the cell cycle, with the highest synthesis occurring in the S period; synthesis was depressed in the M period. Cellular glycoprotein was synthesized at approximately the same times as protein, except that the rates of glycoprotein synthesis in the S period relative to other periods were much greater than for protein. Secreted protein was synthesized throughout the cell cycle without any general pattern, except that secretion was elevated in the late S and G₂ periods. Secreted glycoprotein was similar to secreted protein. Cellular lipid and cellular glycolipid were synthesized almost exclusively in the G₂ and M periods; there was no synthesis in the G₁ and S periods. Release or secretion of glycolipid and lipid also occurred in the G₂ and M periods.     

Myeloid Cells Restrict MCMV and Drive Stress-Induced Extramedullary Hematopoiesis through STAT1

1. Download high-res image (263KB)
2. Download full-size image