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Biomedical subjects

F Kovacs

Publications and source records attributed to F Kovacs.

11 recordsLinked to original sources
PubMed2006

Distribution and elimination of fumonisin analogues in weaned piglets after oral administration of Fusarium verticillioides fungal culture.

The distribution and elimination of fumonisins after oral administration of 50 mg FB(1), 20 mg FB(2) and 5 mg FB(3) per animal day(-1) for 22 days was studied in weaned barrows. At the end of the trial, the lung, heart, liver, kidney, spleen, brain, serum, bile, muscle, fat, urine and faeces samples were collected and their content of fumonisins (FB(1), FB(2)) determined by LC-MS. The highest FB(1) concentrations were found in the liver (99.4 +/- 37.5 ng g(-1)) and kidneys (30.6 +/- 10.1 ng g(-1)), whilst the highest average amount of FB(2) was in the liver (1.4 +/- 2.3 ng g(-1)) and fat (2.6 ng g(-1) +/- 4.8) samples. Comparing the FB(1)/FB(2) ratio in different organs (19/1), it was found that the ratio in the abdominal and subcutaneous fat samples (4/1) was markedly different from those in all other tissues, namely the relative proportion of FB(2) was higher in latter cases. Of the total quantity of FB(1), the 13% taken up during 5 days was excreted unchanged with the faeces and urine. On average, in the urine and faeces, FB(1) was detected in nine- and 14-fold quantities, as compared with FB(2).

Adipose Tissue↗
PubMed2001

Structure of the transmembrane region of the M2 protein H(+) channel.

The transmembrane domain of the M2 protein from influenza A virus forms a nearly uniform and ideal helix in a liquid crystalline bilayer environment. The exposure of the hydrophilic backbone structure is minimized through uniform hydrogen bond geometry imposed by the low dielectric lipid environment. A high-resolution structure of the monomer backbone and a detailed description of its orientation with respect to the bilayer were achieved using orientational restraints from solid-state NMR. With this unique information, the tetrameric structure of this H(+) channel is constrained substantially. Features of numerous published models are discussed in light of the experimental structure of the monomer and derived features of the tetrameric bundle.

Influenza A virus↗
PubMed2000

Imaging membrane protein helical wheels.

Resonance patterns have been observed in 2D solid-state NMR spectra of the transmembrane segment of M2 protein from Influenza A virus in oriented samples reflecting the helical wheel of this alpha-helix. The center of this pattern uniquely defines the helical tilt with respect to the bilayer normal without a need for resonance assignments. The distribution of resonances from amino acid specific labels around the "PISA wheel" defines the rotational orientation of the helix and yields preliminary site-specific assignments. With assignments high-resolution structural detail, such as differences in tilt and rotational orientation along the helical axis leading to an assessment of helical coiling, can be obtained.

Influenza A virus↗
PubMed1999

Validation of the single-stranded channel conformation of gramicidin A by solid-state NMR.

The monovalent cation selective channel formed by a dimer of the polypeptide gramicidin A has a single-stranded, right-handed helical motif with 6.5 residues per turn forming a 4-A diameter pore. The structure has been refined to high resolution against 120 orientational constraints obtained from samples in a liquid-crystalline phase lipid bilayer. These structural constraints from solid-state NMR reflect the orientation of spin interaction tensors with respect to a unique molecular axis. Because these tensors are fixed in the molecular frame and because the samples are uniformly aligned with respect to the magnetic field of the NMR spectrometer, each constraint restricts the orientation of internuclear vectors with respect to the laboratory frame of reference. The structural motif of this channel has been validated, and the high-resolution structure has led to precise models for cation binding, cation selectivity, and cation conductance efficiency. The structure is consistent with the electrophysiological data and numerous biophysical studies. Contrary to a recent claim [Burkhart, B. M., Li, N., Langs, D. A., Pangborn, W. A. & Duax, W. L. (1998) Proc. Natl. Acad. Sci. USA 95, 12950-12955], the solid-state NMR constraints for gramicidin A in a lipid bilayer are not consistent with an x-ray crystallographic structure for gramicidin having a double-stranded, right-handed helix with 7.2 residues per turn.

Gramicidin↗
PubMed1999

Correlations of structure, dynamics and function in the gramicidin channel by solid-state NMR spectroscopy.

The high resolution structure of the gramicidin A channel has been determined in a lamellar phase environment using solid-state NMR spectroscopy. While the fold is similar to previous characterizations, channel function is exquisitely dependent on structural detail. There is essentially no structural change upon cation binding and no significant change in dynamics. The cations appear to be adequately solvated in their binding site by no more than two carbonyls and no fewer than three water molecules at any one time. The relatively large number of water molecules allows for geometric flexibility and little selectivity among monovalent cations. However, the dehydration energies of cations clearly explain the selectivity for monovalent versus divalent cations. Moreover, the binding site is shown to be delocalized, resulting in a shallow potential energy well so that efficient cation conductance can be realized. The potential energy barrier at the bilayer centre has been shown to be rate limiting under certain circumstances through a correlation between conductance and the electrostatic interactions between cations at the gramicidin monomer-monomer junction and the indole dipole moments at the lipid-water interface. The dynamics are functionally important. The time-scale for carbonyl fluctuations about the C alpha-C alpha axis and kinetic rates for cation movement in the channel are the same, suggesting a correlation between molecular dynamics and kinetics. These functional correlations will be described in light of the recent K+ channel structure and the biological challenge to achieve both selectivity and efficiency.

Amino Acid Sequence↗
PubMed1996

Conformational trapping in a membrane environment: a regulatory mechanism for protein activity?

Functional regulation of proteins is central to living organisms. Here it is shown that a nonfunctional conformational state of a polypeptide can be kinetically trapped in a lipid bilayer environment. This state is a metastable structure that is stable for weeks just above the phase transition temperature of the lipid. When the samples are incubated for several days at 68 degrees C, 50% of the trapped conformation converts to the minimum-energy functional state. This result suggests the possibility that another mechanism for functional regulation of protein activity may be available for membrane proteins: that cells may insert proteins into membranes in inactive states pending the biological demand for protein function.

Magnetic Resonance Spectroscopy↗
PubMed1990

Role of prestomal teeth in feeding of the house fly, Musca domestica (Diptera; Muscidae).

Ultrastructural studies of the mouthparts of Musca domestica L. show that the fly's prestomal teeth are more damaging to host tissues than considered previously. When fed on tissue culture or pig cornea, SEM revealed that M. domestica were able to tear and suck up cells. This process occurs so rapidly, and so few cells are involved, that the damage is not perceptible to the naked eye. Except for the prestomal teeth, the mouthparts have few other structures which can inflict the damage observed.

Animals↗