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K Gersonde

Publications and source records attributed to K Gersonde.

At least 55 records · Page 3Linked to original sources
PubMed1985

Identification and characterization of tissues by T2-selective whole-body proton NMR imaging.

T2-selective proton imaging at 10 MHz is based on a Carr-Purcell-Meiboom-Gill pulse sequence with at least 36 echoes and 2 tau greater than or equal to 6 ms employing the projection reconstruction technique. The transverse magnetization decay of the volume elements is multiexponential composed of up to three monoexponential T2 components. The T2 values are arranged in T2 histograms which are slice specific. T2 windows are defined in the T2 histogram and used for imaging and for selecting T2 values which are assigned to proton classes and tissues. Tissue characterization is based on the visualization of differences in T2 behavior. The T2 values are transformed into 256 gray levels or, by use of a red-green-blue lookup table, into a rainbow code. Two display techniques have been developed and implemented in the RWTH Aachen Magnetic Resonance Software System (RAMSES): (i) for nonselective T2 imaging with secondary T2 selection and encoding of molecular classes on the basis of T2 values; (ii) for T2-selective imaging by employing combined primary and secondary T2 selection and encoding particular tissues and variations therein. The tissues can be identified by selecting different classes of molecules, like water, lipids, and proteins, when shifting the primary T2 window on the T2 axis of the T2 histogram.

Adult↗
PubMed1985

Continuous gas-depletion technique for measuring O2-dissociation curves of high-affinity hemoglobins.

The O2-depletion technique allows a continuous measurement of the complete O2-dissociation curve of high-affinity hemoglobins in the O2-partial pressure range of 700 to 10(-4) mm Hg. With this technique p50 values greater than or equal to 0.01 mm Hg (approximately equal to 1.3 Pa) can be determined for 3-microliter hemoglobin samples. As examples, O2-dissociation curves of sperm whale myoglobin (p50 = 0.9 mm Hg, 25 degrees C, pH 8.0) and Dicrocoelium hemoglobin (p50 = 0.06 mm Hg, 25 degrees C, pH 4.9) are demonstrated which show Hill coefficients of n = 1.0 over the complete O2-saturation range.

Animals↗
PubMed1984

Assignment of the Fe-N epsilon (His) stretching mode in the resonance Raman spectra of a monomeric insect cyanomethaemoglobin.

Resonance Raman (RR) spectra of the monomeric cyanomethaemoglobin CTT III from insect larvae of Chironomus thummi thummi are shown for the range of 200-550 cm-1. By iron and cyanide isotope exchange a line varying between 307 cm-1 for 57Fe-13C15N and 311 cm-1 for 54Fe-12C14N, has been assigned to the Fe-N epsilon stretching mode of this haem complex. The substitution of 54Fe for 57Fe has no effect on the Fe-C = N bending mode whereas it affects the Fe-CN stretching mode.

Animals↗
PubMed1984

Analysis of multiple T2 proton relaxation processes in human head and imaging on the basis of selective and assigned T2 values.

Two-dimensional T2-selective proton imaging of human head has been performed at 10 MHz employing Carr-Purcell-Gill-Meiboom pulse trains with echo separation of 6 and 12 msec. Using the information of 36 spin echoes and applying a recovery time of 2 sec the magnetization decay has been traced. The multi-exponential T2 relaxation curve of each pixel of the image has been deconvoluted into up to three mono-exponential functions which are defined by 1/T2,i and alpha i. The T2,i values are represented in a T2 histogram of the slice and then selected for generating images which relate to protons with specific T2. The alpha i values indicate the relative amounts of the T2-selected protons. Imaging on the basis of alpha i values increases the contrast of the image. The multiple T2-selective imaging technique leads to head images which show selectively cerebrospinal fluid, gray matter, different types of white matter, and nonassigned fast-relaxing proton classes.

Brain↗
PubMed1984

Iron-carbon bond lengths in carbonmonoxy and cyanomet complexes of the monomeric hemoglobin III from Chironomus thummi thummi: a critical comparison between resonance Raman and x-ray diffraction studies.

Soret-excited resonance Raman spectroscopy yields direct information regarding the iron-carbon bonding interactions in the cyanomet and carbonmonoxy complexes of hemoglobin III from Chironomus thummi thummi (CTT III) in solution. By isotope exchange in cyanide (13CN-, C15N-, and 13C15N-) and carbon monoxide (13CO, C18O, and 13C18O), we have assigned the Fe(III)-CN- stretching at 453 cm-1, the Fe(III)-C-N- bending at 412 cm-1, the Fe(II)-CO stretching at 500 cm-1, the Fe(II)-C-O bending at 574 cm-1, and the C-O stretching at 1960 cm-1. The resonance Raman data, in conjunction with those obtained from heme model complexes with well-known Fe-C bond distances, strongly suggest that the Fe(III)-CN- bond (approximately 1.91 A) is longer (hence weaker) than the Fe(II)-CO bond (approximately 1.80 A). This result disagrees with those of x-ray crystallographic studies [Steigemann, W. & Weber, E. (1979) J. Mol. Biol. 127, 309-338] in which the Fe-C bond lengths were reported as 2.2 A in cyanomet and 2.4 A in carbonmonoxy CTT III. Based on Badger's rule and normal mode calculations, the x-ray data would lead to the prediction of 279 cm-1 for the Fe(II)-CO stretching frequency in CTT III . CO, which was not observed. On the other hand, we estimate the Fe-CO bond as approximately equal to 1.82 A, which is very similar to the 1.80-A value in human Hb . CO crystals. Furthermore, we have used isotope shift data to estimate the Fe-C-O angle as 169 +/- 5 degrees, somewhat larger than the 161 degrees value found by Steigemann and Weber. We therefore conclude that there must be errors in the x-ray crystallographic refinement for the ligand geometry in carbonmonoxy and cyanomet CTT III.

Animals↗
PubMed1983

High-resolution proton NMR as indicator of a silent mutation in the haem cavity of a monomeric allosteric haemoglobin.

Comparison of the high-field 1H-NMR spectra of the met-cyano complexes of allosteric haemoglobins III and IV of the insect larva Chironomus thummi thummi (CTT-III and CTT-IV) shows that, in addition to the molecular heterogeneity previously described for both Hbs as due to haem orientational disorder [La Mar et al. (1980) J. Biol. Chem. 255, 66-70], CTT-III but not CTT-IV exhibits a second heterogeneity as evidenced by splitting of numerous signals. Reconstitution of CTT-III with modified haems alters the populations of the two haem rotational isomers but leaves the secondary heterogeneity unaffected. This argues directly for locating this secondary heterogeneity solely within the polypeptide chain rather than the result of protein-haem interaction. We assign this secondary heterogeneity found solely in Hb-III to a point mutation in the haem cavity, 57E6 (Ile/Thr); CTT-IV is chemically homogeneous. The observation of significant hyperfine shift differences for the alternative substitution at 57E6, particularly for non-haem single-proton resonances thought to arise from distal residues, indicates some structural consequences in the haem cavity due to the point mutation. While a difference in the allosteric properties cannot be detected in that the point mutation appears to leave the pK for the allosteric transition unaltered, subtle influences on the function of the protein in both affinity states cannot be ruled out at this time.

Allosteric Regulation↗
PubMed1982

Bohr-effect and pH-dependence of electron spin resonance spectra of a cobalt-substituted monomeric insect haemoglobin.

The monomeric haemoglobin IV from Chironomus thummi thummi (CTT IV) exhibits an alkaline Bohr-effect and therefore it is an allosteric protein. By substitution of the haem iron for cobalt the O2 half-saturation pressure, measured at 25 degrees C, increases 250-fold. The Bohr-effect is not affected by the replacement of the central atom. The parameters of the Bohr-effect of cobalt CTT IV for 25 degrees C are: inflection point of the Bohr-effect curve at pH 7.1, number of Bohr protons -- deltalog p1/2 (O2)/deltapH = 0.36 mol H+/mol O2 and amplitude of the Bohr-effect curve deltalogp1/2 (O2) = 0.84. The substitution of protoporphyrin for mesoporphyrin causes a 10 nm blue-shift of the visible absorption maxima in both, the native and the cobalt-substituted forms of CTT IV. Furthermore, the replacement of vinyl groups by ethyl groups at position 2 and 4 of the porphyrin system leads to an increase of O2 affinities at 25 degrees C which follows the order: proto less than meso less than deutero for iron and cobalt CTT IV, respectively. Again, the Bohr-effect is not affected by the replacement of protoporphyrin for mesoporphyrin or deuteroporphyrin. The electron spin resonance (ESR) spectra of both, deoxy cobalt proto- and deoxy cobalt meso-CTT IV, are independent of pH. The stronger electron-withdrawing effect by protoporphyrin is reflected by the decrease of the cobalt hyperfine constants coinciding with gparallel = 2.035 and by the low-field shift of gparallel. The ESR spectra of oxy cobalt proto- and oxy cobalt meso-CTT IV are dependent of pH. The cobalt hyperfine constants coinciding with gparallel - 2.078 increase during transition from low to high pH. The pH-induced ESR spectral changes correlate with the alkaline Bohr-effect. Therefore, the two O2 affinity states can be assigned to the low-pH and high-pH ESR spectral species. The low-pH form (low-affinity state) is characterized by a smaller, the high-pH form (high-affinity state) by a larger cobalt hyperfine constant in gparallel. The correlation of the cobalt hyperfine constants of the oxy forms with the O2 affinities is discussed for several monomeric haemoglobins. The Co-O-O bond angle in cobalt oxy CTT IV is characterized by an ozonoid type of binding geometry and varies little during the pH-induced conformation transition. Due to the lack of the distal histidine in CTT IV no additional interaction via hydrogen-bonding with dioxygen is possible; this is reflected by the cobalt hyperfine constants.

Animals↗
PubMed1981

Proton nuclear magnetic resonance investigation of the nature of solution conformational equilibria of monomeric insect deoxyhemoglobins.

The proton nuclear magnetic resonance spectra of the three monomeric deoxyhemoglobins of the insect larva Chironomus thummi thummi have been recorded, assigned, and analyzed. In the two allosteric hemoglobins, the heme methyls and vinyl protons were assigned by specific deuterium labeling. The hyperfine-shifted proximal histidyl imidazole exchangeable protons for the three native and two deuteroheme-reconstituted hemoglobins were assigned by comparison of spectra in H2O and 2H2O. Both native and reconstituted allosteric hemoglobins exhibit two sets of interconvertible resonances indicative of two heme orientations differing by a 180 degrees rotation about the alpha-gamma-meso axis, as previously found for the met-cyano analogues [La Mar, G. N., Smith, K. M., Gersonde, K., Sick, H., & Overkamp, M. (1980) J. Biol. Chem. 255, 66]. The relative pH sensitivities of the heme resonance hyperfine shifts for the two allosteric hemoglobins and the apparent pK approximately 8 indicate that the t in equilibrium r allosteric transition, as modulated by the Bohr proton, is being observed. For the native hemoglobins, the t in equilibrium r conformational transition was found to be centered at the heme periphery, with the proximal histidyl imidazole environment insensitive to both pH and the rotational position of the heme, consistent with the absence of a pH influence on the ligation on-rate. For the deuteroheme-reconstituted allosteric hemoglobins, both the heme and axial imidazole environments sense the t in equilibrium r transition, and the histidine environments for the two components for each hemoglobin can be clearly distinguished, suggesting that the ligation on-rates may depend on both pH and heme orientation.

Animals↗
PubMed1979

Co-binding studies on Hb M Iwate. Allostery of a T state haemoglobin.

The mutant haemoglobin Hb M Iwate alpha 2Mmet87His leads to Tyr beta 2, is characterized by a stable T structure and a low ligand affinity. Sigmoidal CO-binding isotherms of symmetrical shape with Hill coefficients of n = 1.4 at pH 6 to n = 1.9 at pH 10 and the differences in the mean affinity (PCO(1/2)) and the affinity of the first ligand-binding beta subunit (1/L1 greater than Pco(1/2)) are the evidence for the cooperativity. The comparison of the Bohr effects of the two valency hybrid states (alpha 2Mmet beta met beta deoxy alpha 2Mmet beta 2deoxy) in the absence of and in the presence of polyphosphates leads to an indirect proof of pH-dependent subunit-subunit interaction. Inositol hexaphosphate-binding suppresses cooperativity in the pH range 5.5-8 (n = 1). Above pH 8 hte cooperativity increases to a final value of n = 1.9 at pH greater than 10, which is identical to that of stripped Hb M Iwate. The CO binding to the first binding site exhibits a Bohr effect. Polyphosphate anions have no influence on the CO binding of the first binding site. The heterotropic effects are discussed as intrachain effects (Bohr effect of the first binding site) and interchain effects (Bohr effect of Pco(1/2); influence of polyphosphates).

Allosteric Regulation↗
PubMed1979

Incorporation of inositol hexaphosphate into intact red blood cells. I. Fusion of effector-containing lipid vesicles with erythrocytes.

Fluid charged lipid vesicles loaded with an inositol hexaphosphate solution were used to transport this allosteric effector into human intact red blood cells. Rate and extent of uptake of the vesicles and of the effector by the red blood cells were measured as changes in the O2 half-saturation pressure and the 31P-NMR spectra of the intracellular inositol hexaphosphate-haemoglobin complex.

Erythrocytes↗
PubMed1979

Incorporation of inositol into intact red blood cells. II. Enhancement of gas transport in inositol hexaphosphate-loaded red blood cells.

The gas-transport function of red blood cells which have incorporated inositol hexaphosphate is significantly improved by fusion with effector-loaded lipid vesicles. "Right-shifts" of the O2-binding curves of inositol hexaphosphate-loaded red blood cells with half-saturation pressures at 37 degrees C up to 98 mmHg are observed. The transformation of 56% of the intracellular haemoglobin into the low affinity state corresponds to an optimum increase of the O2-release capacity of 270%. The CO2 transport is also correspondingly enhanced. The treated red blood cells show no inositol hexaphosphate depletion during a reasonable time.

Carbon Dioxide↗
PubMed1979

Improvement of the red blood cell O2 release capacity by lipid vesicle-mediated incorporation of inositol hexaphosphate.

Fusion of unilamellar lipid vesicles with red blood cells has been used to deliver entrapped inositol hexaphosphate (IHP) to the cells. Incorporated IHP tightly bound to hemoglobin produces a significant and lasting "right-shift" of the O2-binding curve of red blood cells. The O2 release capacity of red blood cells is increased by this method up to 270% of the normal value. The Bohr effect is increased so that carbon dioxide transport is also enhanced. The fine structure of the erythrocytes does not seem to be altered by the lipid vesicle incorporation.

Erythrocytes↗
PubMed1978

Acid Bohr effects in myoglobin characterized by proton NMR hyperfine shifts and oxygen binding studies.

Proton NMR studies of sperm whale and horse deoxymyoglobin have revealed that both proteins exhibit a single, well defined, pH-induced structural change. The changes in hyperfine shifts are clearly observed not only at the heme peripheral substituents, but also at the proximal histidyl imidazole, which suggest that heme-apoprotein contacts are looser in the acidic than alkaline conformations. The hyperfine shift changes are modulated by a single titratable group with a pK of approx. 5.7 in both proteins. Oxygen binding studies of sperm whale myoglobin over a range of temperature and pH showed that, while the oxygen affinity was independent of pH at 25 degrees C, it increased below pH 7 at 0 degrees C and decreased below pH 7 at 37 degrees C. Hence, sperm whale myoglobin exhibits a small acid Bohr effect which most likely arises from the characterized structural changes in the deoxy proteins. While horse myoglobin failed to exhibit a resolvable acid Bohr effect between 0 and 37 degrees C, it did show a weak alkaline Bohr effect at 25 degrees C which disappeared at lower temperatures. Since the oxygen affinity changed smoothly over several pH units, this alkaline Bohr effect can not be associated with any well defined conformational change detected by NMR.

Animals↗