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At least 1,081 records · Page 60Linked to original sources
PubMed1979

Fibrinogen: agreement of experimental and calculated hydrodynamic data with electron-microscopic models.

There is no general agreement on the size and shape of the fibrinogen molecule. We have studied the diffusion of the fibrinogen in solution by means of dynamic light scattering, nanosecond fluorescence depolarization and analytical ultracentrifugation. The results obtained under physiological concentration, pH an ionic strength are DT = 2.0 X 10(7) cm2sec-1, DR perpendicular = 40'000 sec 1. Nanosecond fluorescence depolarization yielded DR parallel = 1.6 x 10(6) sec-1. Tentatively this value is interpreted as DR parallel, namely rotational diffusion about the major axis of the molecule. The sedimentation coefficient is 8.1 S. The hydrodynamic parameters derived from our measurements were compared with those calculated on the basis of the models proposed by Hall and Slayter, Hudry-Clergeon and Marguerie et al., Bachmann and Lederer, and Köppel. The agreement is poor even if the degree of hydration is varied within wide limits. However, satisfactory agreement can be achieved by assuming a flexible molecule of about 900 A length corresponding to two end-to-end bound trinodular structures of the Hall and Slayter type, with a nodule diameter of about 45 A. Experimental evidence indicates that the discrepancies between the different models might be due to different techniques of sample preparation leading to different conformations of the molecule.

Fibrinogen↗
PubMed1978

The non-tubulin component of microtubule protein oligomers. Effect on self-association and hydrodynamic properties.

We have investigated the association of non-tubulin microtubule proteins with tubulin to form the ring-shaped oligomeric structures found in microtubule preparations. We have found that the two oligomeric species present in our preparations of microtubule protein (s020,w = 18 and 30 S) each require non-tubulin factors for their formation. Two types of non-tubulin protein, the high molecular weight proteins (HMW) and the tau proteins were found to be active in ring formation. The HMW proteins promoted the formation of the 30 S oligomer, while the tau proteins promoted the formation of an oligomer of s020,w = 20 S. Analysis of the 30 S oligomer by gel filtration chromatography showed that the ratio of HMW proteins to tubulin was about twice that in the microtubule. The HMW proteins could be destroyed by exposure to trypsin, resulting in a marked increase in the sedimentation coefficient of the 30 S oligomer to 39 S. The 20, 30, and 39 S species were identified as rings by electron microscopy. The identity of the 18 S structure as a ring was called into question. Our data indicate that the 20 S species is a single ring and that the 30 S oligomer is a two-layered ring bearing HMW projections which contribute substantial hydrodynamic drag to the particle. We compare the organization of tubulin subunits and HMW molecules in the 30 S ring with the organization of these components in the microtubule and suggest that the organization in the ring is conserved in the microtubule.

Animals↗
PubMedDate not supplied

[Hydrodynamic stands for testing assisted circulation and artificial heart apparatus].

Problems arising in devising the assisted circulation apparatus and artificial heart can be solved only with investigations conducted on hydrodynamic models of the circulation system--the stands. An analysis of literature sources dealing with test stands justifies their classification according to the purpose, the types of tests, the specific structure and basic characteristics. It is necessary to proceed with further improvement of the stand equipment in the direction of creating a sufficiently accurate imitation of the anatomic structure and resilient properties of major arteries and veins, of constructing a geometrical and elastic model of the aorta, of pressure and flow control instruments at different points of the vessels, of the ones regulating the energy parameters, as well as of working out criteria for effectiveness of the devices to be used.

Assisted Circulation↗
PubMed1980

Hydrodynamic properties of the regulatory component of adenylate cyclase.

Hydrodynamic parameters of the regulatory component of adenylate cyclase, G/F, have been estimated by gel filtration and sucrose density gradient centrifugation. In solutions containing Lubrol 12A9, the protein has an apparent molecular weight of 130,000. G/F from various sources and resolved from the catalytic moiety of the enzyme by different techniques behaves similarly. Consistent with our previous proposal that this protein is the site of action of both guanine nucleotides and fluoride, treatment with these activating ligands causes a reduction in both the sedimentation coefficient and the Stokes radius of G/F. These changes suggest a loss of mass of approximately 40,000 daltons. Nevertheless, this alteration is fully reversible when ligands are removed, even if the liganded protein is first fractionated by gel filtration or sucrose density gradient centrifugation.

Adenylyl Cyclases↗
PubMed1983

Structural characterization of insulin receptors. I. Hydrodynamic properties of receptors from turkey erythrocytes.

Insulin receptors from turkey erythrocyte plasma membranes were solubilized in nondenaturing detergents (Triton X-100 and sodium deoxycholate). Their hydrodynamic properties were determined by sedimentation analyses in H2O and D2O, and gel filtration on Sepharose 4B. Two specific insulin-binding species are observed after velocity sedimentation in linear sucrose density gradients: peaks I and II. In Triton X-100, the sedimentation coefficient (s20,w), partial specific volume (Vc), and Stokes radius (a) for peaks I and II are, respectively, 10.2 +/- 0.5 S and 6.6 +/- 0.5 S, 0.75 +/- 0.02 ml/g, and 0.76 +/- 0.02 ml/g, and 89 +/- 3 A and 76 +/- 3 A, to yield Mr = 410,000 +/- 75,000 and 235,000 +/- 55,000, respectively, for the protein-Triton X-100 complex. The corresponding values in deoxycholate solution are: 10.7 +/- 0.5 S and 6.9 +/- 0.5 S, 0.71 +/- 0.03 ml/g and 0.70 +/- 0.04 ml/g, and 86 +/- 3 A and 69 +/- 3 A for peaks I and II, respectively, to yield 360,000 +/- 65,000 and 180,000 +/- 45,000, respectively, for the molecular weight of the protein-deoxycholate complex. These data are consistent with a model whereby each receptor species binds to one micelle of the appropriate detergent. In agreement with this model, it was also found that, in both Triton X-100 and deoxycholate, concentrations higher than the critical micellar concentration are required in order to maintain discrete receptor species in solution. At concentrations below the critical micellar concentration, the receptors aggregate to a broad band that sediments faster than 11.3 S. This is typical of membrane proteins that are stabilized in solution by insertion into detergent micelles. Based on these results, the protein molecular weights of peaks I and II are estimated to be 355,000 +/- 65,000 and 180,000 +/- 45,000, respectively. When membranes are treated with the reducing agent dithiothreitol, peak I is converted to peak II. This fact, together with the estimates obtained for the protein molecular weights of the two receptor species, suggests that peak I is a disulfide-linked dimer of peak II. The sedimentation characteristics of insulin receptors in many different cell types appear to be similar. As with turkey erythrocytes, detergent extracts of membranes from rat liver contained two native receptor species whose sedimentation coefficients were similar to peaks I and II. However, in all the other cell types examined, including rat adipocytes, rat heart muscle, 3T3-L1 adipocytes, 3T3-C2 fibroblasts, and FAO hepatoma cells, peak I (the native dimer) was the predominant species observed.

Animals↗
PubMed1978

[Comparative hydrodynamic study of artificial heart valves in pulsating flow].

A comparative hydrodynamic study of artificial heart valves with spherical, hemispherical and lentil-shaped obturative elements has been carried out under the non-stationary conditions. The valves resistance coefficient is higher in the lentil-shaped valves. With the increase of pulse rate the stroke volume of the valves of all the types drops, and the regurgitation increases.

Aortic Valve↗
PubMed1984

[Changes in the hydrodynamic resistance of collaterals after ligation of the femoral artery].

After ligation of the femoral artery in 12 dogs anatomical changes of the collaterals 1 month after the operation are accompanied with 18-fold decrease of hydrodynamic resistance in them as compared to the initial one. The shifts observed in 96% are the results of dilatation occurring in the intramuscular interarterial anastomoses. Dilatation of the intramuscular arteries, situating more distally to the anastomosis zone and experiencing a decreased arterial pressure, is also observed, as it is in proximal vessels, situating in the zone of an increased blood pressure. Despite the essential shifts, the blood flow capacity of the collaterals even 1 month after the operation is still 500 times as small as that of the intact femoral artery.

Animals↗
PubMedDate not supplied

[Flow-type cuvette of an optical analyzer with hydrodynamic focusing of the liquid under study].

Described in the paper is a flow cuvette (probe) for an optical analyzer of formed blood elements and other cell suspensions. The cuvette is provided by hydrodynamic focusing of the liquids. The cuvette differs from the commonly known models by the following parameters: a high upper limit of the operating range for the Reynolds number and, as a result, the possibility to increase the analysis rate, high spatial and time resolution, and compactness.

Blood Cell Count↗
PubMed1978

[New procedure for protein spinning: the hydrodynamic process].

In this text, we describe a new protein spinning process called hydrodynamic process. Parameters which are related to production of fibers and which can influence diameter and texture are explained extensively. In this process, a spinning dope is extruded through a spinnerette in a moving coagulation bath in which the fibers are coagulated, stretched and carried.

Dietary Proteins↗
PubMed1978

In vitro hydrodynamic comparison of mitral valve prostheses at high flow rates.

A pulse duplicator system for evaluating the hemodynamic performance of mitral prostheses is described. Under conditions stimulating normal resting physiology, all valves tested had measurable but acceptably small pressure drops. Under conditions simulating exercise, all were moderately to severely stenotic. Valves with nearly equal mounting diameters were compared. The Hancock, Beall, and Starr-Edwards valves (Group A) were found to be significantly more stenotic than the Björk-Shiley, Cutter-Cooley, Ionescu-Shiley, and Lillehei-Kaster valves (Group B). In the 29 to 30 mm. mounting diameter size at cardiac outputs of 5 and 9 L. per minute, Group A had average pressure drops of 3.2 and 10.5 mm. Hg and Group B, pressure drops of 1.6 and 5.3 mm. Hg, respectively. In the 24 to 26 mm. mounting diameter size, at cardiac outputs of 9 L. per minute, all the valves had critically large pressure drops (9 to 17.6 mm. Hg). The standard Gorlin formula is inappropriate for computing the orifice area of prosthetic valves. The discharge coefficient for a valve (a measure of how well the valve uses its primary flow area) and a performance index (a measure of how well the valve uses its mounting area) have been computed from a knowledge of the orifice size, without the necessity of assuming a value for the discharge coefficient required by the Gorlin formula. The biological valves (Hancock and Ionescu-Shiley) provide an efficient orifice for fluid flow at the free leaflet margins and have large discharge coefficients. On the basis of the fluid dynamic equation of motion, steady flow, root mean square (RMS) flow, and peak flow, combined with the appropriate transvalvular gradients, were all shown to yield equally accurate characterizations of valvular hydrodynamic performance. Mean flow, unfortunately the only value obtainable clinically, yielded effective orifice areas 10 percent smaller than either of the other three flow values.

Bioprosthesis↗
PubMed1978

Simulation of blood flow by a hydrodynamic generator.

Physiological flows are produced by a volumetric gear pump. The motor-pump group is controlled by an amplifying comparator, and produces a flow whose rate follows the control signal. This signal is delivered by a synthetizing generator and its shape, amplitude, and frequency are adjustable. This hydrodynamic generator supplies a test bench on which the modifications of flow patterns induced by models of vascular stenoses are studied. The study of the velocity distribution has been effected with a pulsed-Doppler ultrasonic velocimeter.

Biophysical Phenomena↗
PubMedDate not supplied

[Mathematical modeling of the mechanism of cilia motion: an internal hydrodynamic drive].

A physical approach to the description of the motion mechanism of cilia based on the importance of hydrodynamical interactions between the intraciliary microstructures is proposed. The motion of the cilium model was investigated theoretically. A mechanism of synchronization of cilia beating in metachronal waves is proposed.

Biophysical Phenomena↗
PubMedDate not supplied

[The effect of hydrodynamic conditions on the interferon-synthesizing activity of swine splenocytes in the production of alpha-interferon].

Parameters of physical constituents of the agitation process and mass-exchange characteristics of the suggested bioreactor for suspension cultivation of pig splenocytes are determined. The effect of hydrodynamic conditions on viability and interferon-synthesizing activity of cells in production of alpha-interferon of pigs has been studied. The relation existing between interferonogenesis processes proceeding under suspension and under stationary biosynthesis has been analyzed by the pair correlation method.

Animals↗
PubMed1994

Analysis of microtubule rigidity using hydrodynamic flow and thermal fluctuations.

We report the use of two independent new methods to measure the flexural rigidity of microtubules. Microtubules were grown off axonemal pieces adhering to a glass coverslip. In the first method, a hydrodynamic flow was applied to microtubules and the flexural rigidity was derived from the analysis of the bending shape of the microtubules at equilibrium in the flow. In the second method, the flexural rigidity was derived from the thermal fluctuations of the free end of axoneme-bound microtubules. With both methods, the flexural rigidity of standard GDP microtubules was estimated to be 0.85 +/- 0.2 x 10(-23) newtons x m2 which corresponded to a persistence length of 2 +/- 0.2 mm. Binding of ligands known to affect the biochemical properties of microtubules affected their rigidity. The structural analogs of inorganic phosphate AlF4- and [BeF3-, H2O], which bind to the site of the gamma-phosphate of GTP on GDP microtubule and reconstitute the GDP-Pi microtubule intermediate state of GTP hydrolysis, cause an approximately 3-fold increase in microtubule flexural rigidity and persistence length. Taxol and taxotere, antitumoral microtubule-stabilizing drugs, in contrast cause a decrease in flexural rigidity and appear to affect the three-dimensional superstructure of microtubules, which can no longer be considered as semi-flexible rods. The relationship between the mechanical properties of microtubules and their biological function is discussed.

Animals↗
PubMed1993

[Diminished experimental alimentary atherogenesis under the influence of polymers that decrease the hydrodynamic resistance of the blood].

The experiments on adult rabbits have demonstrated that high-cholesterol diet given to the animals for 3 months causes a severe hypercholesterolemia and disseminated aortic lesion due to the formation of numerous fatty streaks and plaques of atherosclerotic genesis. The simultaneous intravenous injection of a special linear high molecular-weight polymer solution, which reduces hydrodynamic resistance once a week leads to a significantly less atherogenesis in the same hypercholesterolemia. The highest effect was observed in the descending portions of the aorta and just after its bifurcation, i.e. in the areas of the least unsteady blood flow.

Animals↗
PubMed1994

Comparative study of the hydrodynamic function of the size 19mm and 21mm St. Jude Medical Hemodynamic Plus Bileaflet Heart valves.

The hydrodynamic function of the St. Jude Medical Hemodynamic Plus Bileaflet Heart valve has been compared to the function of the standard St. Jude valve, the Carbomedics, Duromedics and the Monostrut valves in a pulsatile flow simulator. Size 19mm and 21mm tissue annulus diameter valves have been studied for use in small aortic roots. The size 19mm St. Jude hemodynamic Plus had lower forward flow pressure drops and lower total energy losses than the other valves studied. The size 19mm St. Jude Hemodynamic Plus valve should provide lower forward flow pressure drops and energy losses for the patient with a small aortic root, than the other types of prostheses included in the study.

Aortic Valve↗
PubMedDate not supplied

[The hydrodynamic evaluation of some types of aortocoronary bypass].

Liquid flow in cylindrical and converging transplants for aortocoronary bypass, in intricately branching vascular systems were experimentally studied by polarization optic method using "jumping" aortocoronary shunts and different flow regimens, sites and severity of vascular stenosis. Hydrodynamic advantages of conic shunts in comparison with cylindrical ones were revealed, the rest shunting conditions being equal. It was found that when "jumping" shunts are used the distal portion of the coronary artery which is shunted the first should not be dilated by more than 50%. The end anastomosis should be formed with the artery more significant for myocardial blood supply.

Anastomosis, Surgical↗