PubMed Health⌕ Search

Biomedical subjects

S Fazekas

Publications and source records attributed to S Fazekas.

At least 19 recordsLinked to original sources
PubMed2006

Morphologies of three-dimensional shear bands in granular media.

We present numerical results on spontaneous symmetry breaking strain localization in axisymmetric triaxial shear tests of granular materials. We simulated shear band formation using the three-dimensional distinct element method with spherical particles. We demonstrate that the local shear intensity, the angular velocity of the grains, the coordination number, and the local void ratio are correlated and any of them can be used to identify shear bands; however, the latter two are less sensitive. The calculated shear band morphologies are in good agreement with those found experimentally. We show that boundary conditions play an important role. We discuss the formation mechanism of shear bands in the light of our observations and compare the results with experiments. At large strains, with enforced symmetry, we found strain hardening.

Journal Article↗
PubMed2005

Piling and avalanches of magnetized particles.

We performed computer simulations based on a two-dimensional distinct element method to study granular systems of magnetized spherical particles. We measured the angle of repose and the surface roughness of particle piles, and we studied the effect of magnetization on avalanching. We report linear dependence of both angle of repose and surface roughness on the ratio f of the magnetic dipole interaction and the gravitational force (interparticle force ratio). There is a difference in avalanche formation at small and at large interparticle force ratios. The transition is at f(c) approximately 7. For f < f(c) small vertical chains follow each other at short times (granular regime), while for f > f(c) the avalanches are typically formed by one single large particle-cluster (correlated regime). The transition is not sharp. We give plausible estimates for f(c) based on stability criteria.

Journal Article↗
PubMed2003

Two-dimensional array of magnetic particles: the role of an interaction cutoff.

Based on theoretical results and simulations, in two-dimensional arrangements of a dense dipolar particle system, there are two relevant local dipole arrangements: (1) a ferromagnetic state with dipoles organized in a triangular lattice and (2) an antiferromagnetic state with dipoles organized in a square lattice. In order to accelerate simulation algorithms, we search for the possibility of cutting off the interaction potential. Simulations on a dipolar two-line system lead to the observation that the ferromagnetic state is much more sensitive to the interaction cutoff R than the corresponding antiferromagnetic state. For R approximately > 8 (measured in particle diameters) there is no substantial change in the energetical balance of the ferromagnetic and antiferromagnetic state and the ferromagnetic state slightly dominates over the antiferromagnetic state, while the situation is changed rapidly for lower interaction cutoff values, leading to the disappearance of the ferromagnetic ground state. We studied the effect of bending ferromagnetic and antiferromagnetic two-line systems and observed that the cutoff has a major impact on the energetical balance of the ferromagnetic and the antiferromagnetic state for R approximately < 4. Based on our results we argue that R approximately 5 is a reasonable choice for dipole-dipole interaction cutoff in two-dimensional dipolar hard sphere systems, if one is interested in local ordering.

Journal Article↗
PubMed1997

Symptom distress three months after heart transplantation.

BACKGROUND: Although symptoms of heart failure abate after heart transplantation, other symptoms caused by the surgery, immunosuppressant drugs, and complications can be new sources of symptom distress for patients after operation. METHODS: This two-site National Institutes of Health study compared symptom distress in 173 adult heart transplant recipients from before operation to 3 months after operation. The Heart Transplant Symptom Scale was used to measure 92 symptoms related to heart disease and heart failure, transplantation, medication side effects, and complications commonly found in this population. Analysis was via paired t tests with Bonferroni correction. Most patients (93%) were receiving a triple immunosuppressant regimen of cyclosporine, azathioprine, and prednisone. RESULTS: Total symptom distress decreased significantly (p = 0.013) from before operation to 3 months after heart transplantation. The 23 symptoms that decreased the most (p = 0.000) after operation accounted for a cumulative total reduction of 583% less symptom distress. These symptoms were primarily cardiopulmonary, neuromuscular, and emotional. The 10 symptoms that worsened the most (p = 0.000) after operation accounted for a cumulative total increase of 284% more symptom distress. These symptoms were primarily dermatologic, neurologic, and gastrointestinal and were all side effects of prednisone and cyclosporine. CONCLUSIONS: The net change in symptom distress resulted in 299% less symptom distress in this cohort at 3 months after heart transplantation. This significant improvement in symptom outcomes scientifically documents the effectiveness of heart transplantation in reducing symptoms of heart failure, along with accompanying emotional symptoms. These research findings therefore reinforce and support the positive symptom outcomes often reported anecdotally in clinical practice.

Adult↗
PubMed1990

The comparative morphology of the muscle tissues and changes in constituents in the pig types.

The authors have revealed the main value characteristics of pork production by testing in five different types of pig the volume of contractile and collagen proteins, that of proteoglycans, the constituents of blood and the enzymes of the blood plasma. The contractile proteins of the muscle tissues basically determine the quality of pork. The same applies to the water retention capacity, colloidal characteristics and glycogen content of meat. The amount of contractile proteins has decreased in the best meat producing types of pig. Parallel with the decrease of white meat, and with the increase in the volume of ham, chop and chuck the contractile protein content of muscles decreased. The scientific fact according to which there is a certain correlation among the changes in the volume of contractile proteins, blood sugar level, blood serum CPK and the intensity of activity of the LDH enzymes promotes the qualifying of live animals and the work of the geneticists aiming at the increasing of the contractile protein content of the muscle tissues of pigs by selection. According to tests carried out by us the primary cause of PSE changes is a decreased volume of contractile proteins. Increased stress sensitivity and all the other factors have but a secondary importance and are all consequential. The decrease in the quantity of contractile proteins or--it is better to put it this way--the lack of the proper amount of such proteins characterizing a fully developed pig's organism is caused by the nowadays usual breeding technologies and can be well explained by those selection activities which aim at a one-sided kind of pork production.

Animals↗
PubMed1989

[Molecular mechanisms of muscle contraction].

Studying the mechanism of muscular contraction not even in one of the cases deriving from 50 sources could be obtained a myosin preparation free of phosphate. Therefore the aim of the authors was to elaborate methods which provided means for producing preparations of an endogenous P content that approached the P content of myosins of live sources. The phosphoryl groups of myosin may be released by incubating these preparations with F-actin. The actin attaches to the interaction domain of myosin and upon its effect P migrates within the myosin molecule from the site of phosphorylation to the interaction domain. At the interaction the myosin attaches to the actin through the phosphoryl group subsequently the myosin head turns from 90 degrees to 45 degrees consequently the actin-filament moves to a 12 mm distance towards the center of the sarcomer. When the myosin-actin-phosphoryl bridge ceases to be the P attaches transiently to the actin and the anorganic phosphate releases from the actin. The active center of myosin is filled again with the gamma phosphoryl group of ATP and the head returns simultaneously to the resting position of 90 degrees.

Animals↗
PubMed1989

Presence of phospho-tyrosine in alkaline hydrolysate of pig skeletal muscle myosin.

A small part of the P-containing fraction of myosin hydrolysate which could be eluted with basic solvent (triethylamine) buffer was accumulated on chromatographic column. On the basis of the elution profile, P- and tyrosine content determination, moreover the thin layer chromatographic separation and specific Tyr reaction, this fraction is suggested to be phosphotyrosine. The concentration of P-Tyr is about 2 mol in pig muscle myosin calculated for 500 kDa protein. As the higher P-containing myosins also have an approx. 2 mol P-Tyr, it is thought that this concentration had been present in myosins already before alkaline hydrolysis.

Animals↗
PubMed1989

Heterogeneity, distribution and endogenous phosphate content of KCl-myosins prepared from different parts of human brain.

Myosin concentrations and their endogenous phosphate (P) content as well as some of their properties were investigated in different parts of the central nervous system (CNS). Myosin concentration in hemispherial part is in the average 40 mg/100 g fresh mince, but it varies between 5 mg and 30 mg myosin depending on the mental activity or accidental brain diseases. This refers to the other parts of CNS, too. A myosin may be isolated with a single and sharp peak as far as the gel filtration profile is concerned in spite of the high lipid content of the brain. Working with minimal lipid and RNA content requires a careful procedure by an experienced person. In spite of any careful isolation procedure, purified KCl-myosin preparations are composed of at least two isomyosins each formed from different heavy chains. Myosins are localized in different parts of the cell, mitochondrial, synaptosomal and neuroplasmic, respectively. Brain myosins have higher endogeneous P concentrations than other cell-myosins. In hemispherial myosins the P-concentrations are high. Subjects trained in mental activities have the highest myosin and P concentration. We suggest that the role of myosin may directly be connected with cytokinetic motions even in case of the higher functions of brain cells like thinking, paying attention and memory, respectively.

Animals↗
PubMed1988

The effect of terbutaline upon myosin preparations of the human uterus.

It has been perceived that the phosphate (P) content of the human uterus myosin was considerably lower (half or less) in patients treated with terbutaline before delivery than that of untreated patients. Therefore the in vitro effect of terbutaline was investigated upon uterine myosin. The results showed that the presence of terbutaline in the incubation medium without ATP decreased the performed (endogenous) P content of myosin slightly, whereas in the presence of ATP terbutaline facilitated release of the phosphoryl groups from myosin parallel with the increase of terbutaline concentration. Although at low concentrations of terbutaline (in the micromolar range) a few phosphoryl groups are still incorporated in myosin, the time reaching the maximum of P incorporation was prolonged.

Adenosine Triphosphate↗
PubMed1988

A new concept in the molecular process of muscle contraction: functional role of phosphorylated amino acids in myosin.

In this report a summary is given of our experiments concerning the in vivo endogenous phosphate (P) content of myosin. It was found that besides the ester type phosphates of myosin there was a considerable amount of N-P type energy-rich phosphoryl groups bond to the basic amino acids of peptide chains. The endogenous P concentration of myosin depends on the source of the preparation. The concentration of P is much higher in myosin preparations of well-trained animals and human subjects compared to those found in the control muscles. As the P binding sites of fresh purified myosin are only partially saturated, the preparations can incorporate P up to a definite saturation only. The phosphorylating ability of myosins disappears after prolonged storage as a consequence of an alteration in structure of the myosin molecule. The P groups are moving inside the myosin molecule. It is supposed that the inorganic P release promoted by actin is connected with the thin filament movements towards the centre of the sarcomere, furthermore P replenishment, P linking and movement involve N3-trimethyl-lysine, 3-methylhistidine, P-Arg and two conformers of P-His. The two net negative charges of P group form electric monopoles of a minor battery (myosin head). They help to force generation at head rotation (90 degrees-45 degrees angle) and produce free energy changes that can be calculated from the number of N-P bonds.

Amino Acids↗
PubMed1988

Purification, phosphate content and phosphorylation of myosin from human vascular smooth muscle.

Myosin was prepared from human umbilical artery and some of its properties were studied. The yield of myosin after ultracentrifugation was 4.3-13.6 mg/gr wet weight of tissue (mean: 8.6 mg/gr). A considerable amount of phosphate bound to the myosin was found in all preparations. Phosphate content of umbilical arterial myosin was higher than what had been found in our earlier works in skeletal muscle myosin. Phosphate content of umbilical arterial myosin also could be further increased by incubation in ATP containing media. While the rate of phosphorylation of human umbilical arterial myosin was slower than that of skeletal muscle myosin, the saturated phosphate levels reached with 0.5 mM ATP concentration were higher for vascular myosin. The slower phosphate uptake rate of vascular myosin may be related to the slower contraction rate of this muscle type. After alkaline hydrolysis of lipid free myosin, 7 or 8 peaks of N-phosphoryl amino acids and phosphorylated amino acid derivates could be separated by ion exchange chromatography.

Adenosine Triphosphate↗
PubMed1987

Autophosphorylation of untrained and well-trained skeletal muscle myosin.

Earlier the autophosphorylation of myosin and the labile phosphate (P) content of rabbit skeletal muscle was reported [6, 7, 9]. The present paper describes that the endogeneous preformed P level in fresh preparation of exercised muscle is higher than that of untrained control one. It was revealed that the presence of a significant amount of mitochondrial myosin (with much higher P content) in the well-trained human muscle preparations falsified the appreciation of myofibrillar myosin. Therefore, a reliable myofibrillar preparation with correct P content from exercised subjects was obtained only after the separation of mitochondrial fraction. The P content of fresh preparations can be increased by phosphorylation even in the exercised muscle myosins up to the most higher level in human samples. The phosphoryl group incorporation from [gamma-32P]ATP into the rabbit and hare myosins was checked by radioactive tracer technique, and confirmed by total P content determination performed parallel with molybdate test. It was stated that under present circumstances the labelled 32P incorporation was lower even at an optimal substrate concentration than that of P value obtained directly with molybdate method; because the total P content of preparations had not exchanged during 2 min incubation. So it has been concluded from [gamma-23P] phosphoryl group assayments that much higher amount of P was incorporated into P-Arg, N pi-P-His and fraction 2 as compared with unappreciated labelled P level of the inorganic P (P-Ser, P-Thr), P-Lys, N tau-P-His and minor fractions. From these observations it has been considered that the P-Arg, N pi-P-His and fraction 2 take part in the contraction mechanism and in the course of physical training.

Adenosine Triphosphate↗
PubMed1987

Preparation and characterization of mitochondrial myosins of rat and human liver.

This paper confirmed the reality of the mitochondrial myosin (mt-myosin in human and rat liver. Simultaneously, cytoplasmic myosin (cp-myosin) was prepared from the large particle-free supernatant. The yield of purified mt- and cp-myosin from 1 kg fresh liver was altogether 5-600 mg (= 1-1.2 mumol). Half of the myosin originated from the mitochondrial fraction (composed of about 60 g of mitochondrial protein), while the remaining portion (cp-myosin) was derived from a translucent, but voluminous supernatant (containing about two-third of liver proteins). Comparing the molecular mass of mt- and cp-myosin to the skeletal muscle myosin (about 480 kDa)--on the basis of gel filtration profiles--they proved to have similar profiles. The characteristic properties of both preparations were similar to other myosins developing filamentous aggregations and showing ATP-induced superprecipitations, but they had lower ATPase activities thus being more similar to smooth muscle and cell myosins than to skeletal muscle myosin. The mitochondria and both myosins contained abundant covalently bound P and their endogeneous Si content was low, 2-3 mumol/g in fresh mitochondria and 5-7 mol Si per mol in the mt-myosin. The Si content was resolved into 2-3, while P into 5-6 fractions as revealed by ion exchange chromatographic technique. The mt-myosin could be saturated to a higher P level by autophosphorylation than the cytoplasmic myosin. The interaction of actin with myosin induced a release of significant amounts of P, depending on the ATP concentration. The Cu2+ treatment of mt-myosin caused also P release, and a limited amount of Cu remained bound in the preparations.

Actins↗
PubMed1987

Presence of covalently bound energy-rich phosphates in human tracheal smooth muscle myosin.

In a preliminary report, the tracheal NaCl-myosin prepared from an old and a young subject was discussed. In the present paper, the total bound phosphate (P) content and its distribution is described in two parallel preparations of human muscle myosin. It was shown that a considerable amount of covalently bound P was present not only in NaCl, but in the fresh preparations of tracheal KCl-myosin. Analysing this phosphate fraction in the alkaline hydrolysate of RNA- and lipid-free preparations of myosin it was confirmed that phosphate was linked to the basic amino acid residues and their hydrolytic derivatives. As the phosphoryl binding sites are partly saturated, the phosphate concentration can be enhanced nearly three-fold compared to the fresh preparation. Phosphate incorporation is an autophosphorylation process depending on the ATP and Mg2+ concentration. Studying the actomyosin fraction in the presence of ATP it was found that its phosphate content can also be increased to a certain degree. It is supposed that the changes in phosphate content of myosin are associated with the formation of crossbridges between the actin and myosin filaments in the processes of muscle contraction and relaxation. The process can be influenced directly and indirectly by some natural factors and drugs resulting in the concentration or relaxation of bronchial muscles.

Actomyosin↗
PubMed1986

Preparation and P content of non-pregnant and pregnant human uterine myosin.

Myosin content and phosphorus (P) concentration of myosin preparations were measured in non-pregnant and pregnant human myometrial tissue specimens. It was found that the amount of myosin gained from 1 g of minced myometrial tissue is 0.5 mg in the early follicular phase of the menstrual cycle, 0.6-0.7 mg in the late luteal phase, and 6-7 mg during pregnancy. Considering the different functional stages of the myosin sources and the performance characteristics of the methods, the estimated myosin content of non-pregnant myometrium is 1.0-1.5 mg, while 10-15 mg in pregnant myometrial tissue. A considerable amount of P is bound to the preparations. It is the smallest in the post-menstrual period and increases towards the end of the cycle. The largest amount of P is gained from fresh pregnant uterine samples. Analysis of the alkaline hydrolysate showed that the phosphate group was bound to amino acids, in the largest amount to arginine, less to histidine and the smallest amount to lysine and serine. As a function of the duration of storage, especially the P-Arg concentration was decreasing. The prolonged hydrolysis time decreases again the concentration of P-Arg with a consecutive increase of No. 1 and 2 P-containing peaks in the chromatographic profile of alkaline hydrolysate.

Chromatography, Gel↗
PubMed1985

Purification and properties of myosin from the "hatching muscle" (m. complexus) of geese.

The present work is concerned with the study of myosin fractions prepared from the hatching muscle (m. complexus) and a control muscle (m. pectoralis) of the developing goose embryo. The m. complexus attained its maximum mass at hatching and in the 4-day-old bird the mass of this muscle was only one fourth of that recorded at hatching. The m. complexus was hypertrophied already on the 21st day. At days 21, 27 and 28 of incubation and at posthatching days myosin preparations were made from both muscles. Partial purification of myosins from both sources yielded a high molecular weight fraction characteristic of the adult bird and one other protein fraction with molecular mass half of myosin. Both preparations exhibited the characteristic properties of myosin. The lower molecular weight fraction was also shown to develop filamentous aggregates as did the higher molecular-weight, gel filtrated myosin. The phosphate content of the half molecular mass myosin fraction prepared from the embryonic m. complexus at days prior to hatching was considerably higher than that of the high molecular weight fraction and the predominant component was P-Arg. Since the embryonic myosin was still not available in the m. complexus of the 4-day-old birds and the hypertrophied muscle underwent regression after hatching it appears that this myosin fraction is actively involved in breaking through the shell during the hatching period in geese.

Adenosine Triphosphatases↗
PubMed1985

Preparation and characterization of myosin from cultured cells of Escherichia coli (02:K1 30156 strain).

In this study the myosin preparations isolated from E. Coli cell cultures were analysed. The isolation of myosin from fresh cultures resulted in a substantially higher (approximately 10-fold) yield than from stored cells. The coli myosin, despite the two DEAE-cellulose treatments, contained more RNA and P-lipid than the myosin prepared from skeletal muscle. The RNA content can be removed gradually by acetone denaturation and lipid removal followed by subsequent washings. The fresh preparations contained protein-bound alkali-stable P; part of this was released by Cu ions. The coli myosin can be phosphorylated. The phosphate uptake depended on the concentrations of ATP and Mg2+ and on the time of incubation. The alkaline hydrolysate of the phosphorylated, washed lipid-free preparation was resolved into 8 P-containing peaks on ion-exchange chromatography. Of fractions P-Arg, Pi, P-Lys and 2 P-His conformer were identified by means of synthetic compounds, elution pattern and specific reactions. The remaining compounds could not be identified. The most abundant component was P-Arg suggesting that this compound might play an important role in the cytokinetic movements of E. coli.

Adenosine Triphosphate↗