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Biomedical subjects

D F Wallach

Publications and source records attributed to D F Wallach.

At least 127 records · Page 7Linked to original sources
PubMed1974

Focal erythrocyte membrane perturbations caused by nitroxide lipid analogues.

Three classes of lipoidal nitroxide spin probes reversibly perturb erythrocyte membranes at low concentrations (10(-10)-10(-5) M). This is manifest in (a) decreased osmotic fragility and (b) alterations of surface topology. At bulk phase nitroxide concentrations providing maximal osmotic stabilization, the erythrocytes exhibit a classic echinocyte morphology. At nitroxide concentrations very slightly higher than those yielding minimal osmotic fragility (10(-5)-10(-4) M), the cellus undergo a sphering reaction and lyse. The morphologic sequence seen in intact cells is not observed in erythrocyte ghosts. We suggest that the spin probes initially concentrate in focal domains, which expand into echinocytic protrusions primarily due to localized weakening of membrane cohesion. We propose that cell lysis involves an irreversible breakdown in membrane domain structure.

Cell Membrane↗
PubMed1974

Reversible, thermotropic alteration of nuclear membrane stucture and nucleocytoplasmic RNA transport in Tetrahymena.

We examine the effect of cooling upon the freeze-etch ultrastructure of nuclear membranes, as well as upon nucleocytoplasmic RNA transport in the unicellular eukaryote Tetrahymena pyriformis. Chilling produces smooth, particle-free areas on both faces of the two freeze-fractured macronuclear membranes. Upon return to optimum growth temperature the membrane-associated particles revert to their normal uniform distribution and the smooth areas disappear. Chilling lowers the incorporation of [(14)C]uridine into whole cells and their cytoplasmic RNA. Cooling from the optimum growth temperature of 28 degrees to 18 degrees C (or above) decreases [(14)C]uridine incorporation into cells more than into their cytoplasmic RNA; chilling to below 18 degrees C but above 10 degrees C causes the reverse. [(14)C]Uridine incorporation into whole cells and their cytoplasmic RNA reflects overall RNA synthesis and nucleocytoplasmic RNA transport, respectively. RNA transport decreases strongly between 20 degrees and 16 degrees C, which is also the temperature range where morphologically detectable nuclear membrane transitions occur. This suggests that the nuclear envelope limits the rate of nucleocytoplasmic RNA transport at low temperatures. We hypothesize that a thermotropic lipid phase transition switches nuclear pore complexes from an "open" to a "closed" state with respect to nucleocytoplasmic RNA transport.

Animals↗
PubMed1973

Membrane optical activity: some facts and fallacies.

The circular dichroism of hypothetical, water-filled, spherical shells, 75-3500 nm in radius, with walls 7.5 nm thick, composed of poly(L-lysine) in various conformational proportions, and suspended in water, were computed from the known optical properties of this polypeptide by classical general light-scattering theory (Mie theory). Comparison of the computed curves of circular dichroism spectra with those of diverse membranes reveals large discrepancies below 215 nm and shows that light scattering does not adequately account for the optical activity of membranes containing appreciable proportions of nonhelical conformation. However, turbidity effects can explain the anomalies of membrane optical rotatory dispersion near 233 nm, if not uniquely so. We conclude that the optical activity of neither most soluble proteins nor membrane proteins can provide accurate conformational information when synthetic polypeptides are used as standards and list the reasons for this argument. We also show that present techniques to "correct" membrane optical activity are likely to produce additional artifact.

Animals↗
PubMed1973

Temperature-induced variations in the surface topology of cultured lymphocytes are revealed by scanning electron microscopy.

Temperature-induced variations in the surface morphology of cultured lymphocytes were evaluated by scanning electron microscopy. At 25-37 degrees the cells' surfaces are largely obscured by numerous undulating microvilli of various lengths but uniform diameter. Temperature changes alter the number of microvilli, their lengths, diameters, distribution, branching, and fusing. Typically, chilling to 0-4 degrees markedly reduces the number of microvilli and increases the diameter of the survivors in a reversible process. In contrast, heating the cells to about 45 degrees rapidly and irreversibly transforms the ordinarily smooth membrane surface into one with a "cobblestone" morphology. At the same time most microvilli disappear and the few that remain clump into a cap. The data suggest that the low-temperature effects reflect a change in the physical state of membrane lipids, while the high-temperature alterations represent thermotropic protein transitions.

Animals↗