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M J Costello

Publications and source records attributed to M J Costello.

52 records · Page 3Linked to original sources
PubMed1982

On the structural organization of isolated bovine lens fiber junctions.

Junctions between fiber cells of bovine lenses have been isolated in milligram quantities, without using detergents or proteases. The structure of the isolated junctions has been studied by thin-section, negative-stain, and freeze-fracture electron microscopy and by x-ray diffraction. The junctions are large and most often have an undulating surface topology as determined by thin sectioning and freeze-fracture. These undulations resemble the tongue-and-groove interdigitations between lens fiber cells previously seen by others (D. H. Dickson and G. W. Crock, 1972, Invest. Ophthalmol. 11:809-815). In sections, the isolated junctions display a pentalamellar structure approximately 13-14 nm in overall thickness, which is significantly thinner than liver gap junctions. Each junctional membrane contains in the plane of the lipid bilayers distinct units arranged in a square lattice with a center-to-center spacing of 6.6 nm. Freeze-fracture replicas of the junctions fractured transversely show that the repeating units extend across the entire thickness of each membrane. Each unit is probably constructed from four identical subunits, with each subunit containing a protein of an apparent molecular weight of 27,000. We conclude that the lens junctions are structurally and chemically, different from gap junctions and could represent a new kind of intercellular contact, not simply another crystalline state of the gap junction protein.

Animals↗
PubMed1981

Effects of n-alkanes on the morphology of lipid bilayers. A freeze-fracture and negative stain analysis.

The effect of n-alkanes on the ultrastructure of lipid bilayers has been investigated using freeze-fracture and negative stain electron microscopy. It has been found that the morphology of bilayers containing the long alkane tetradecane is quite different from bilayers containing the short alkane hexane. The smooth fracture faces of gel and liquid crystalline state bilayers are unmodified by tetradecane. However, hexane dramatically alters the hydrophobic bilayer interior, producing large (20 to 50 nm) mounds and depressions in the fracture faces. The fracture steps in these multilayer preparations containing hexane are variable in thickness and often considerably wider than the corresponding fracture steps in multilayers which contain tetradecane or are solvent-free. Alkanes also modify the structure of the P beta' or 'banded' phase of phosphatidylcholine bilayers. The incorporation of tetradecane removes the banded structure from both the bilayer's hydrophilic surface, as viewed by negative staining, and the bilayer's hydrophobic interior, as viewed by the freeze-fracture technique. These results are consistent with X-ray diffraction data which imply that long alkanes are primarily located between adjacent lipid hydrocarbon chains in each monolayer of the bilayer, while short alkanes can partition into the geometric center of the bilayer between apposing monolayers.

Alkanes↗
PubMed1981

Ultrastructure of hemoglobin-depleted human erythrocyte resealed ghosts.

Both negative-stain and freeze-fracture electron microscopic techniques revealed that the ultrastructure of resealed white ghosts prepared at high dilution during the hemolysis step is very different from that of resealed ghosts prepared at low or moderate dilution (pink ghosts). The negative-stained resealed white ghosts showed light halo substructures on membrane surfaces and protrusions at the edge of the ghosts. Freeze-fracturing of these ghosts showed that membrane blebbing had occurred and that fragments of the membranes resealed to form small right-side-out vesicles ranging from 0.1 to 0.3 micrometer in diameter.

Erythrocyte Membrane↗
PubMed1980

Effect of dietary arginine level on urinary orotate and citrate excretion in growing kittens.

Three experiments were conducted to examine the effect of dietary arginine on urinary orotic acid excretion and the relationship between orotic aciduria and the cat's dietary arginine requirement. In the first experiment, diets containing 1.66 or 0.83% arginine were compared for their ability to sustain growth and food intake and prevent orotic aciduria. Growth and food intake were similar for each diet but the cats fed the 0.83% arginine excreted seven times as much orotic acid as those fed the 1.66% arginine. In the second experiment, diets containing 0.2, 0.4, 0.6, 0.8 and 1.0% arginine were compared for their ability to support growth and food intake and to prevent citric and orotic aciduria. Growth and food intake were optimized with arginine as 0.8% of the diet. Over the range of 0.4--1% arginine, orotic acid excretion was inversely related to the level of arginine, also orotate excretion of cats fed all levels of arginine was greater than that recorded in cats given 1.66% dietary arginine. The estimated level of dietary arginine required to minimize orotic acid excretion was 1.05%, which is 0.3% in excess of that required for maximum growth. Citrate excretion did not respond to dietary arginine level. In the third experiment, cats receiving a commercial cat food containing 1.74% arginine did not show orotic aciduria.

Aging↗
PubMed1980

Ultra-rapid freezing of thin biological samples.

Miniature thermocouples are used to follow the time course of cooling within test samples plunged into liquid coolants. Variations in the temperature and type of coolant (propane, Freon 22, sub-cooled liquid nitrogen), in the velocity and depth of plunge, and in the size and shape of samples were investigated. Coolants have their optimum cooling properties at their lowest liquid temperatures but show different dependencies on temperature. The optimum velocity of plunge depends on the shape of the sample. The strongest influence on cooling rate comes from the size and shape of the sample. Spherical samples about 1 mm3 show rates < 500 decrees C/s while samples 0.001 mm3 show rates > 50,000 degrees C/s for freezing in liquid propane under identical conditions. Thin samples of equivalent volume can be more rapidly frozen. Cooling rates of about 11,900 degrees C/s (0 degrees C to -100 degrees C) are recorded for thin samples (0.1 mm3 and 20 micrometers thick) sandwiched between copper strips and rapidly plunged into liquid propane (-190 degrees C). An apparatus is described for using these holders in freeze-fracture studies. Thin samples thus frozen show no evidence of ice crystal growth in either low-temperature x-ray diffraction patterns or in freeze-fracture electron micrographs.

Freeze Fracturing↗
PubMed1978

The direct measurement of temperature changes within freeze-fracture specimens during rapid quenching in liquid coolants.

We have evaluated the cooling rates of specimens mounted in a variety of freeze-fracture holders when plunged into a series of liquid coolants. these rates were measured using miniature thermocouples placed within the mounted specimens. The most rapid cooling rates were obtained using propane at 83 K as the coolant. When mounted on a newly devised 'copper sandwich' holder, specimen cooling rates in excess of 4500 K/s have been recorded. A simple guillotine-like device for quenching freeze-fracture specimens under reproducible conditions is presented.

Chlorofluorocarbons, Methane↗
PubMed1978

The use of low temperature X-ray diffraction to evaluate freezing methods used in freeze-fracture electron microscopy.

Two methods of freezing samples for freeze-fracture electron microscopy have been compared using X-ray diffraction and freeze-fracture results from lipid-water model systems. Perturbations of the molecular organization of hydrocarbon chains and the extent of ice crystal formation have been evaluated for lamellar phases of egg lecithin containing 16% water and egg lecithin-phosphatidylinositol containing 55% water, both freeze quenched in liquid Freon-22 near its melting temperature (113 K). Very thin samples sandwiched between copper sheets separated by an electron microscope grid show much less freezing induced structural rearrangement than small smaples contained on conventional Balzers-type gold planchettes. These results show that the rate of freezing in the very thin preparations is greater than in the conventional ones, which is probably due in part to the improved dissipation of heat from a poorly conductive sample through highly conductive copper sheets.

Freeze Fracturing↗
PubMed1976

Correlated x-ray diffraction and freeze-fracture studies on membrane model systems. Perturbations induced by freeze-fracture preparative procedures.

Lipid-water and protein-lipid-water phases have been examined by X-ray methods before and after freezing. Frozen samples have been subsequently fractured and replicated, thus permitting an evaluation of the nature of structural perturbations in samples examined by freeze-fracture electron microscopy. Important results are summarized: (1) Freezing low water content (approx. less than 25%) phases causes perturbations in the packing of hydrocarbon chains. The results suggest that freezing liquied paraffin chains produces a condensed "glass-like" packing. (2) Additional perturbations occur in high water content samples. After freezing, much smaller lamellar repeat distances, intense ice reflections, and extensive perturbation of fracture faces are consistant with the expulsion of water from between lamellae. Presence of glycerol generally relieves these perturbations but in some cases introduces additional lattice disorder. (3) Surprisingly, cooling by a stream of cold N2 gas (-140 degrees C) produces qualitatively the same results as rapid cooling in liquid Freon-22 (-160 degrees C). (4) Complex perturbations occur in phases containing integral membrane proteins. Interesting results have been obtained with cytochrome b5-lecithin lamellar associations which display both smooth and rough fracture faces without clearly defined particles.

Binding Sites↗
PubMedDate not supplied

Cytochrome oxidase: structural insights from electron microscopy and from secondary structure prediction.

Electron microscopic images of selectively contrasted cytochrome oxidase dimer crystals are interpreted in a manner consistent with the structure of monomers determined by Fuller et al. (J. Molec. Biol. 134, 305-327). The arms of the y-shaped monomers lie within and perpendicular to the lipid bilayer protruding approximately 25 A on the matrix side of the membrane. The cytoplasmic-side tails of two monomers spread apart in a dimer forming a large cleft. Decoration of the exposed matrix side of vesicle crystals with antisubunit IV antibody fragments indicates that subunit IV lies along the a-crystal axis roughly 20 A from the center of the dimer. A membrane propensity algorithm applied to the sequences of cytochrome oxidase subunits predicts a total of 19 transmembrane alpha-helices per monomer.

Binding Sites, Antibody↗