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Biomedical subjects

A Elgsaeter

Publications and source records attributed to A Elgsaeter.

At least 37 records · Page 2Linked to original sources
PubMed1985

An electrophoretic device concentrating charged macromolecules to a predetermined final solution volume.

An apparatus for electrophoretic concentration of charged macromolecules to a predetermined final solution volume has been developed. The concentration process has a yield of near 100%, which implies that it is possible to predetermine the final macromolecule concentration as well. Both the final macromolecule solution volume and concentration are nearly independent of the electrophoresis time when it exceeds a certain minimum value. The electric field strength across the boundary containing the concentrated macromolecule solution is very low. This considerably reduces macromolecule aggregation, adsorption, and denaturation at this boundary compared to conventional electrophoretic concentrator designs. Both one-stage and two-stage versions of the apparatus have been developed. The one-stage version easily yields a 10-fold and the two-stage version a 50-fold concentration of the macromolecules. Typical macromolecule solution start volumes are 20-50 ml.

Electrochemistry↗
PubMed1985

Human erythrocyte spectrin dimer intrinsic viscosity: temperature dependence and implications for the molecular basis of the erythrocyte membrane free energy.

We have determined experimentally the temperature dependence of human erythrocyte spectrin dimer intrinsic viscosity at shear rates 8-12 s-1 using a Cartesian diver viscometer. We find that the intrinsic viscosity decreases from 43 +/- 3 ml/g at 4 degrees C to 34 +/- 3 ml/g when the temperature is increased to 38 degrees C. Our results show that spectrin dimers are flexible worm-like macromolecules with persistence length about 20 nm and that the mean square end-to-end distance for this worm-like macromolecules decreases when the temperature is increased. This implies that the spectrin dimer internal energy decreases when the end-to-end distance is increased and that the free energy increase associated with making the end-to-end distance longer than the equilibrium value for the free molecules is of entropic origin. The temperature dependence of the erythrocyte membrane shear modulus reported previously in the literature therefore appears mainly to be due to temperature dependent alterations in the membrane skeleton topology.

Erythrocyte Membrane↗
PubMed1985

Some viscoelastic properties of human erythrocyte spectrin networks end-linked in vitro.

We have succeeded in making macroscopic networks of end-linked human erythrocyte spectrin. The network junctions were made using erythrocyte protein 4.1 irreversibly attached to 5 nm (diameter) colloidal gold particles. Rotary shadowing electron microscopy verifies that the protein 4.1-labelled colloidal gold particles bind only to the tail end of the spectrin molecules. Electron micrographs of protein 4.1-labelled colloidal gold particles incubated at 4 degrees C with spectrin dimers reveal that 1-5 spectrin dimers attach to each protein 4.1-labelled colloidal gold particle yielding a spider-like appearance of these complexes. Incubation with a low concentration of spectrin tetramers instead of dimers leads to extensive formation of spectrin microaggregates whereas use of spectrin concentrations higher than 3 mg/ml and a molar ratio between spectrin tetramers and protein 4.1/Au of 4 leads to formation of macroscopic spectrin networks. We have quantitated the viscoelastic properties of such end-linked macroscopic spectrin networks using a gravitational pendulum viscoelastometer. We find that in vitro end-linked spectrin networks can be described by linear viscoelastic theory. The dynamic storage modulus increases almost linearly with the spectrin-protein 4.1/gold particle concentration when the spectrin concentration exceeds about 3 mg/ml and the molar ratio between spectrin tetramers and protein 4.1/Au is 4. At a spectrin concentration of 6 mg/ml and the same ratio between spectrin and protein 4.1/Au, we find a dynamic storage modulus at low frequency of about 80 dyn/cm2. This is in adequate agreement with what is predicted by simple elastomer theory.

Blood Proteins↗
PubMed1985

A computerized low-shear pendulum viscoelastometer, stress-relaxation, shear creep, and dynamic elastic moduli measurements of soft biogels.

A computerized low-shear pendulum viscoelastometer that is well suited for measurements of the viscoelastic properties of soft biogels is described. The instrument has three modes of operation: (i) measurement of dynamic elastic moduli, (ii) stress relaxation, and (iii) shear creep-creep recovery. The main mechanical parts of the instrument include a specimen cuvette and a pendulum with a thin metal plate extending into the specimen cuvette. The cuvette and pendulum can undergo independent angular movements relative to a horizontal axis located about 12 cm above the specimen cuvette. The absolute angular position of the cuvette is under on-line computer control through a stepping motor driven micrometer. The angular position of the pendulum relative to the cuvette is measured using an inductive position detector. The necessary software for automatic operation, data acquisition and processing has been developed for all the three modes of operation. The instrument is well suited for measurements of dynamic elastic moduli in the range 0.02-150 dyn/cm2. Calibration data obtained using 100% ethanol are presented. The instrument suitability for measurements of stress relaxation and shear creep-creep recovery is illustrated by presenting the results of such measurements on a 5.5-mg/ml erythrocyte spectrin gel in isotonic solution.

Biophysical Phenomena↗
PubMed1985

A practical, high-resolution, microcomputer-based method for the analysis of relaxation data exhibiting multicomponent exponential decays.

We have developed and tested a practical, rapid, high-resolution, microcomputer-based method for the analysis of multicomponent exponential decays. The analysis utilizes the Fourier deconvolution technique and includes methods to reduce noise both in the input data and in the results. The developed method is particularly well suited for analysing decays consisting of a wide range of decay times. The method resolves two exponential decays differing by a factor of two when the input data are mathematically generated and without noise, and resolves two decays differing by a factor of three when 2% Gaussian noise is present in the same data. The method lends itself to routine analysis of any relaxation process consisting of exponential decays, including biomedical applications such as enzyme kinetics, circulatory transport functions, pharmacokinetics, plasma exchange therapy, and analysis of compartmental models for any process.

Birefringence↗
PubMed1984

An electro-optic study of human erythrocyte spectrin dimers. The presence of calcium ions does not alter spectrin flexibility.

In order to determine whether the presence of Ca2+ increases the stiffness of the highly elongated and flexible spectrin molecules, we have carried out a birefringence relaxation study of isolated human erythrocyte spectrin dimers. Our measurements indicate no significant change in the flexibility of spectrin in solutions containing 0-10(-3) M Ca2+. This finding indicates that decreased spectrin flexibility is not the major functional mechanism underlying the decreased erythrocyte deformability reported as result of elevated intracellular levels of Ca2+. We find that the persistence length of spectrin dimers is less than 20 nm and is not dependent on the Ca2+ concentration.

Calcium↗
PubMed1984

Liquid propane jet-freezing, freeze-drying and rotary replication of the cytoskeleton and plasma membrane associated structures in human monocytes.

We have studied the cytoskeleton and plasma membrane associated structures of human monocytes using liquid propane jet-freezing, freeze-drying and rotary replication. We find that the cytoskeleton of these cells consists mainly of actin filaments. The actin filaments were identified by their ability to bind myosin sub-fragment S1. A large fraction of these actin filaments radiates from dense cytoskeletal foci. The presence of such actin filament rich foci also in unfrozen cells was demonstrated using immunofluorescence light microscopic techniques. In addition to coated pits a network of thin fibrils (diameter 4-5 nm) were observed on the protoplasmic side of the plasma membrane facing the substrate. These results indicate that liquid propane jet-freezing may represent a simple, inexpensive alternative to impact freezing at liquid helium temperature for obtaining the high cooling rate necessary for successful freeze-drying and rotary replication of cytoskeletal structures.

Actins↗
PubMed1982

Theoretical analysis of the ice crystal size distribution in frozen aqueous specimens.

To estimate theoretically how suited different freezing techniques are for freezing of freeze-etch specimens, it is necessary to know the relationship between specimen cooling rate and the resulting average ice crystal size. Using a somewhat simplified theoretical analysis, we have derived the approximate ice crystal size distribution of nonvitrified frozen aqueous specimens frozen at different cooling rates. The derived size distribution was used to calculate the relationship between relative change in average ice crystal size, (delta l/l), and relative change in specimen cooling rate delta (dT/dt)/(dT/dt). We found this relationship to be (delta l/l) = -k X delta (dT/dt)/(dT/dt) where k = 1.0 when specimen solidification takes place at about -6 degrees C, and k congruent to 1.3 when it takes place at about -40 degrees C.

Chemical Phenomena↗
PubMed1982

Theoretical analysis of specimen cooling rate during impact freezing and liquid-jet freezing of freeze-etch specimens.

We have carried out a theoretical analysis of specimen cooling rate under ideal conditions during impact freezing and liquid-jet freezing. The analysis shows that use of liquid helium instead of liquid nitrogen as cooling medium during impact freezing results in an increase in a specimen cooling rate of no more than 30-40%. We have further shown that when both impact freezing and liquid-jet freezing are conducted at liquid nitrogen temperature, the two methods give approximately the same specimen cooling rate under ideal conditions except for a thin outer layer of the specimen. In this region impact freezing yields the highest cooling rate.

Chemical Phenomena↗
PubMed1981

Human spectrin. V. A comparative electro-optic study of heterotetramers and heterodimers.

The electrically induced birefringence of human spectrin heterotetramer and heterodimer solutions at 5 degrees C has been studied. 1. The steady-state birefringence, delta, was found to be approximately proportional to the electric field strength, E, when E greater than or equal to 0.2 kV/mm. For spectrin solutions the specific linear coefficient, delta/(E x c), therefore is a more relevant parameter for describing birefringence saturation behavior when E greater than or equal to 0.2 kV/mm than the commonly used Kerr constant. At 5 degrees C were measured delta/(E x c) = (27 +/- 5) x 10(-8)m4 x V(-1) x kg(-1) for heterodimers and heterotetramers. 2. At 5 degrees C both heterotetramers and heterodimers exhibited more than one birefringence relaxation time and the shortest of these was for both molecules found to be 4.2 +/- 1.0 microseconds. This indicates that the spectrin molecules are highly flexible. The birefringence build-up time for heterotetramers and heterodimers was found to be 20 +/- 7 microseconds and 15 +/- 5 microseconds, respectively.

Birefringence↗
PubMed1981

Human spectrin. VI. A viscometric study.

Employing viscometry, human spectrin heterodimers and heterotetramers were analyzed in aqueous solution containing different amounts of salt. (1) In aqueous 0.1 M NaCl, pH 7.5, at 4 degrees C, the intrinsic viscosity of isolated human spectrin heterodimers and heterotetramers was found to be 40 +/- 6 and 79 +/- 7 ml/g, respectively. (2) The intrinsic viscosity of isolated human spectrin heterodimers and heterotetramers increased to 78 +/- 8 and 180 +/- 10 ml/g, respectively, as the ionic strength of the solution was reduced to about 2 mM. (3) This viscometric study indicates that isolated human spectrin heterodimers and heterotetramers are flexible molecules with a contour length of at least 110 and 200 nm, respectively.

Electrophoresis, Polyacrylamide Gel↗
PubMed1981

A freeze-etch electron microscopic study of liquid propane jet-frozen human erythrocyte membranes.

Freeze-etch electron micrographs of haemolysing erythrocytes and isolated erythrocyte membranes frozen using a liquid propane jet-freezer reveal fracture faces very different from those seen after conventional freezing by dipping the specimens into partly solidified Freon 22. Instead of the rather smooth extracellular fracture faces found after conventional specimen freezing, extracellular fracture faces exhibiting large amounts of fibre-like structures are seen after liquid propane jet-freezing of these specimens. No such structures were found in normal red blood cells. When isolated erythrocyte membranes are frozen under conditions favouring spectrin-actin release, freeze-etch micrographs reveal an apparent continuity between the fibre-like structures on the extracellular fracture face and the long fibre-like structures which extent from the protoplasmic surface of the erythrocyte membrane. These results suggest that liquid propane jet-freezing is capable of revealing a structural difference between the membrane of haemolysing and nonhaemolysed red blood cells, and that this difference is related to the fibrous, peripheral proteins of the membrane.

Erythrocyte Membrane↗
PubMed1981

In situ liquid propane jet-freezing and freeze-etching of monolayer cell cultures.

A procedure for in situ liquid propane jet-freezing of unfixed and unglycerinated monolayer cell cultures is described. We have used the method to study monolayer cultures of rat Sertoli cells and human monocytes. The described procedure gives a cooling rate during specimen freezing high enough to yield adequately frozen specimens even in the absence of any cryoprotectant. Use of the procedure therefore eliminates artefacts usually caused by cell fixation and addition of cryoprotectives.

Animals↗
PubMed1978

Animal carotenoids 15. Carotenoid distribution and carotenoprotein of Asterias rubens.

A clear differentiation in localization according to functional groups in the carotenoids of the starfish, Asterias rubens, is reported. Only the free alpha-ketols, 7,8,7',8'-tetradehydroastaxanthin, 7,8-didehydroastaxanthin and astaxanthin, are present in the purified carotenoprotein. A post mortem liberated slime contained beta,beta-carotene, free and esterified alloxanthin and esterified alpha-ketols. Evidence suggesting the existence of an alloxanthin protein complex was obtained. The carotenoprotein, asteriarubin, accounts for approx. 10% of the protein extracted by low salt dialysis from the purple-blue part of the top skin of A. rubens and exhibits an absorbance maximum at 554 nm in buffer solution. Asteriarubin is a glycoprotein with an equivalent Stoke's radius corresponding to that of globular proteins of molecular weight 8--10 10(4) and contains 20 microgram carotenoid per mg asteriarubin. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of purified asteriarubin disclosed two major components, one of which is a glycopeptide.

Animals↗
PubMed1978

Human spectrin. I. A classical light scattering study.

Human spectrin heterodimers were analyzed in solutions containing different amounts of salt employing the classical light scattering technique. 1. At 22 degrees C the radius of gyration of isolated human spectrin heterodimers in 0.1 M NaCl aqueous solution (pH 7.3) was found to be about 22 nm. 2. The radius of gyration of isolated human spectrin heterodimers was found to increase to about 40 nm as the ionic strength of the spectrin solution (pH 7.3) was reduced to about 1 mM. 3. The light scattering study indicates that the isolated human spectrin heterodimers were highly expanded and flexible molecules with a contour length exceeding about 140 nm.

Adult↗
PubMed1978

Human spectrin. II. An electro-optic study.

The electrically induced birefringence of human spectrin heterodimer solutions has been studied. 1. Human spectrin heterodimers were found to have a specific Kerr constant Bsp = +(5 +/- 2) . 10(-11) m4/(V2 . kg). 2. Human spectrin exhibited a birefringence relaxation time tau decay = (2.0 +/- 0.3) microseconds. 3. The electro-optic study indicates that human spectrin heterodimers have a contour length of more than 40--50 nm.

Birefringence↗