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Biomedical subjects

M H Koch

Publications and source records attributed to M H Koch.

At least 127 records · Page 7Linked to original sources
PubMed1981

Fluctuation x-ray scattering from biological particles in frozen solution by using synchrotron radiation.

Determination of the structure of biological particles, randomly oriented in solution, from spatial correlation analysis of fluctuations in x-ray scattering has recently been proposed. The feasibility of scattering fluctuation measurements was evaluated by using an x-ray synchrotron radiation camera to obtain the spatial correlation for a solution of tobacco mosaic virus along a line. The experimental system, analysis of data, and requirements for the determination of structures in solution are discussed using this example.

Freezing↗
PubMed1980

The use of synchrotron radiation in time-resolved X-ray diffraction studies of myosin layer-line reflections during muscle contraction.

Experiments on striated muscle have been carried out at the EMBL Outstation at DESY, Hamburg, using the electron-positron storage ring DORIS as a high-intensity X-ray source. The low-angle reflections from the myosin cross-bridges could be recorded more than 1,000 times more rapidly than with the best conventional X-ray sources, and could be followed during contraction with a time resolution of 10 ms.

Animals↗
PubMed1980

Stopped-flow x-ray scattering: the dissociation of aspartate transcarbamylase.

A combination of stopped-flow and x-ray scattering techniques was used to study the dissociation of aspartate transcarbamylase (carbamoylphosphate:L-aspartate carbamoyltransferase, EC 2.1.3.2) with a 2:1 excess of p-chloromercuribenzenesulfonic acid (the ratio being calculated on a basis of reactive sites), in the presence and absence of the transition state analogue N-(phosphonacetyl)-L-aspartate. At 10 mg of protein per ml, the scattering curves allowed some details of the reaction to be followed with a time resolution down to 1 sec. The curves showed not only the dissociation of the enzyme complex but also the formation of the subunits. These results show that, with present facilities, x-ray scattering could be used to study dissociation or reassociation reactions with a time resolution of the order of 100 msec.

Allosteric Regulation↗
PubMed1978

Isolation and characterization of phytoferritin from pea (Pisum sativum) and Lentil (Lens esculenta).

Ferritin was isolated from the seeds of pea (Pisum sativum) and lentil (Lens esculenta). The homogeneity of the phytoferritins was established by polyacrylamide-gel electrophoresis. The subunit molecular weights were respectively 20 300 and 21 400 for hte pea and lentil proteins. A neutron low-angle scattering study established the molecular weight of the oligomer as 480 000 for pea apoferritin and 510 000 for lentil apoferritin. Although the quaternary structure of 24 polypeptide chains is preserved, the phytoferritins have a larger cavity in the interior than mammalian ferritins and can thus potentially store 1.2-1.4 times as much iron. The amino acid composition of the phytoferritins show some similarities to those of mammalian apoferritins; tryptic 'fingerprinting' reveals that there are many differences in the amino acid sequence of plant and mammalian apoferritins.

Amino Acid Sequence↗
PubMed1977

Differentiation of opiate and neuroleptic receptor binding in rat brain.

For 6 large series of compounds derived from the piperidine moieties of spiperone, pimozide, haloperidol, pethidine, fentanyl and 4-methocarboxy-fentanyl, IC50 values were determined in the opiate and neuroleptic binding assay using [3H]-fentanyl and [3H]-haloperidol as ligands, respectively. The specificity and difference between both receptors were demonstrated on the basis of several criteria (1) the sterospecificity of the binding (2) the significant correlation between the in vitro activity of the drugs and their pharmacological potency in vivo, not withstanding some discrepancies which are probably of pharmacokinetic and/or metabolic origin (3) the ability to discriminate between morphinomimetic and neuroleptic drugs by the differential affinity for their specific receptro (4) the structure--activity relationships derived from the in vitro data indicating that the structural requirements for high affinity binding in vitro parallel those for high in vivo potency (5) a demonstration, on the basis of physicochemical principles, of the difference in binding mechanism between morphinomimetics and neuroleptics to their respective receptor.

Animals↗
PubMed1977

Contrast variation study of specifically deuterated Escherichia coli ribosomal subunits.

A neutron small-angle scattering analysis has been done on partially deuterated 30S and 50S subunits of Escherichia coli ribosomes by the contrast variation method. The results indicate that the central regions of both particles are RNA-rich whereas their exteriors are protein-rich. The segregation of RNA and protein is much greater in the 50S subunit than in the 30S; the 30S subunit approaches a homogeneous mixture of RNA and protein. In both structures the most probable separation between the centers of mass of their protein and RNA distributions is small, although substantial variation of this parameter is possible within experimental error.

Deuterium↗
PubMed1977

Shape of the 50S subunit of Escherichia coli ribosomes.

Extrapolation of a series of low-angle neutron scattering curves to infinitely high contrast gives a scattering function IC(kappa) which is dependent on the shape of the solute molecule. For the 50S subunit of E. coli ribosomes, the first part of the structure determination by neutron scattering, namely the determination of the molecular shape from IC(kappa), is reported. The result is in good agreement with models of the 50S subunit determined by electron microscopy.

Escherichia coli↗
PubMed1976

New low resolution model for 50S subunit of Escherichia coli ribosomes.

Neutron low angle scattering studies of the 50S subunit of E. coli ribosomes with the contrast variation method reveals large fluctuations in the scattering density. A region of relatively low scattering density, rich in proteins, surrounds an RNA-rich core of higher scattering density. The centers of mass of the RNA and protein parts of the 50S subunit are separated by a distance (20 A) that is considerably smaller than that reported in previous studies.

Escherichia coli↗
PubMedDate not supplied

Structural polymorphisms of rough mutant lipopolysaccharides Rd to Ra from Salmonella minnesota.

The structural polymorphisms of rough mutant lipopolysaccharides (LPS) Rd, Rc, Rb, and Ra from Salmonella minnesota (strains R4, R7, Rz, R5, R345, and R60, respectively) were investigated as a function of temperature, water content, and Mg2+ concentration. The gel to liquid crystalline (beta<==>alpha) phase transition temperature (Tc) and the state of order within each phase were measured by Fourier transform infrared spectroscopy. The amount of bound water was determined by differential scanning calorimetry and the three-dimensional structures in each phase state were characterized by synchrotron radiation X-ray diffraction. The results indicate an extremely complex dependence of the structural behavior of LPS on ambient conditions. The beta<==>alpha acyl chain melting temperatures at high water contents (95-97%), Tc = 31 to 32 degrees C for LPS Rd, 33 to 35 degrees C for LPS Rc to Rb, and 36 degrees C for LPS Ra, increase with decreasing water content and in the presence of Mg2+ cations with a concomitant broadening of the transition range. Below 30 to 50% water content, no distinct phase transitions can be observed. These effects are most pronounced for LPS with the shortest sugar chains. Below 50% water content, only lamellar structures can be observed in the temperature range 5 to 80 degrees C, independent of the Mg2+ concentration. Above 50% water concentration, for large [LPS]:[Mg2+] molar ratios the predominant structure above Tc is nonlamellar; for smaller [LPS]:[Mg2+] molar ratios a superposition of lamellar and nonlamellar structures is found. For all LPS Rd to Rb at low Mg2+ concentrations, the phase transition is connected with a change in the three-dimensional structure from lamellar or mixed lamellar/nonlamellar to a pure nonlamellar, probably cubic structure. The tendency to form non-lamellar structures decreases with the length of the core oligosaccharide. At an equimolar ratio of [LPS] and [Mg2+] a multibilayered organization is observed. Some of the nonlamellar structures are cubic phases with periodicities between 12 and 16 nm. The molecular dimensions of the single endotoxin molecules in the absence and the presence of external water are estimated from the different lamellar periodicities, including those of free lipid A and deep rough mutant LPS Re. These observations are discussed with respect to the biological importance of LPS as a potent inducer of biological effects in mammals.

Bacterial Toxins↗