STUDIES ON PROTEIN UPTAKE BY ISOLATED TUMOR CELLS : II. Quantitative Data on the Adsorption and Uptake of I131-Serum Albumin by Ehrlich Ascites Tumor Cells

Surface adsorption is studied in some detail because it is believed to be a major artifact in measurements of protein uptake by mammalian cells. Adsorption increases linearly with the I131-albumin concentration between 0.001 and 300 mg/ml. After short exposure to 300 mg/ml and two cell washings, the adsorption amounts to 38 mg albumin per gm cell proteins. Further washings remove 80 per cent of this value, leaving a small irreversibly bound residue. At equilibrium, adsorbed albumin can be labeled by a simple albumin exchange. This labeling reaches a steady state within seconds and stays at constant level over 30 minutes. Significant increases above this initial level are measured over periods of 2 hours. In our experimental conditions these increases can be considered due to albumin uptake. This uptake rises linearly with the albumin concentration between 0.5 and 50.0 mg/ml, and reaches 0.2 mg/gm cell protein or 4 x 105 molecules per cell. Compared to the incorporation of free amino acids in similar conditions, this value does not appear to contribute significantly to the N-metabolism of the tumor cells. Adsorption was generally greater than uptake. Both processes are linear functions of the same variable over the whole range of concentration tested. It is suggested that albumin is taken up by pinocytosis

STUDIES ON PROTEIN UPTAKE BY ISOLATED TUMOR CELLS : I. Electron Microscopic Evidence of Ferritin Uptake by Ehrlich Ascites Tumor Cells

Ferritin, added to the incubation medium of ascites tumor cells, was used as an electron microscopic marker to study the uptake of large protein molecules by morphologically intact cells. A definite uptake could be detected after 1 hour of incubation in Tyrode bicarbonate solution containing 0.04 to 13.3 mg ferritin/ml. Ferritin was found in a variety of membrane-surrounded structures, suggesting that pinocytesis and related membrane movements are occurring under physiological conditions and can account for the penetration of intact macromolecules into isolated tumor cells. Supplementation of the medium with serum albumin (33 mg/ml) increased the average amount of ferritin per cell and per pinocytotic structure. Ferritin was strongly adsorbed by fragments of lysed cells, which were readily taken up by intact cells. Besides its role as carrier, this debris appeared to stimulate membrane movements. Only rare examples were found to suggest the release of ferritin from the pinocytotic structures into the cytoplasm. Thus, the disintegration of such structures cannot be considered an obvious step towards a rapid metabolic utilization of protein by the cell. Particles of colloidal gold presented to the cell under the same conditions were not taken up to any significant extent, thus providing good evidence for a selective ingestion of particles of comparable sizes

Majorana quantization and half-integer thermal quantum Hall effect in a Kitaev spin liquid

The quantum Hall effect (QHE) in two-dimensional (2D) electron gases, which is one of the most striking phenomena in condensed matter physics, involves the topologically protected dissipationless charge current flow along the edges of the sample. Integer or fractional electrical conductance are measured in units of $e^2/2\pi\hbar$, which is associated with edge currents of electrons or quasiparticles with fractional charges, respectively. Here we discover a novel type of quantization of the Hall effect in an insulating 2D quantum magnet. In $\alpha$-RuCl$_3$ with dominant Kitaev interaction on 2D honeycomb lattice, the application of a parallel magnetic field destroys the long-range magnetic order, leading to a field-induced quantum spin liquid (QSL) ground state with massive entanglement of local spins. In the low-temperature regime of the QSL state, we report that the 2D thermal Hall conductance $\kappa_{xy}^{2D}$ reaches a quantum plateau as a function of applied magnetic field. $\kappa_{xy}^{2D}/T$ attains a quantization value of $(\pi/12)(k_B^2/\hbar)$, which is exactly half of $\kappa_{xy}^{2D}/T$ in the integer QHE. This half-integer thermal Hall conductance observed in a bulk material is a direct signature of topologically protected chiral edge currents of charge neutral Majorana fermions, particles that are their own antiparticles, which possess half degrees of freedom of conventional fermions. These signatures demonstrate the fractionalization of spins into itinerant Majorana fermions and $Z_2$ fluxes predicted in a Kitaev QSL. Above a critical magnetic field, the quantization disappears and $\kappa_{xy}^{2D}/T$ goes to zero rapidly, indicating a topological quantum phase transition between the states with and without chiral Majorana edge modes. Emergent Majorana fermions in a quantum magnet are expected to have a major impact on strongly correlated topological quantum matter.Comment: 7 pages, 8 figures. Submitted versio

Nontropical sprue with secondary hyperparathyroidism

We have presented the case history of a patient with lifelong, classic nontropical sprue which was previously undiagnosed. She developed secondary hyperparathyroidism with extreme osteitis fibrosa cystica. As do some patients with malabsorption, she presented with musculoskeletal rather than gastrointestinal complaints.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44358/1/10620_2005_Article_BF02235078.pd