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H J Steinhoff

Publications and source records attributed to H J Steinhoff.

35 records · Page 2Linked to original sources
PubMed1992

Temperature-jump studies and polarized absorption spectroscopy of methemoglobin-thiocyanate single crystals.

Association equilibria and association kinetics of the thiocyanate binding reaction to methemoglobin in single crystals and solution are studied using temperature-jump technique and polarized absorption spectroscopy. Different kinetic constants are found for the reaction in solution and crystal phase for the alpha- and beta-subunits of the methemoglobin tetramer. The reduction of the reactivity of the alpha- and beta-subunits in crystalline phase is 6-fold and 2.4-fold, respectively, compared to the values found in solution. The intramolecular binding reaction of the N epsilon of the distal histidine E7 which is observed in methemoglobin in solution cannot be detected in single crystals. Our results suggest that crystallization of hemoglobin has little influence on small-scale structural fluctuations which are necessary for ligands to get to the binding sites and large-scale structural motions are suppressed.

Animals↗
PubMed1992

Structural fluctuations and conformational entropy in proteins: entropy balance in an intramolecular reaction in methemoglobin.

The reversible intramolecular binding of the distal histidine side chain to the heme iron in methemoglobin is of special interest due to the very large negative reaction entropy which overcompensates the large reaction enthalpy. It may be considered as a prominent example of the ability of proteins (including enzymes) to provide global entropy in a local process. In this work new experiments and model calculations are reported which aim at finding the structural elements contributing to the reaction entropy. Geometrical studies prove the implication of the 20 residue E-helix being shifted by more than 2 A. Vibrational entropies are calculated by a procedure derived from the method of Karplus and Kushik. It turns out that neither the histidine alone nor the complete E-helix contribute more than 15 per cent of the required entropy.

Amino Acid Sequence↗
PubMed1991

A new method for the determination of the permittivity of small samples in the microwave range and its application to hemoglobin single crystals.

A cavity perturbation method for the absolute determination of the complex permittivity of small samples in the microwave range is developed and tested. Samples with volumes less than 0.4 mm3, for example protein powder or single crystals of macromolecules, may be investigated in a temperature range between 180 and 300 K, using this method. As an application the complex permittivity of hemoglobin single crystals is determined at three frequencies, v = 3.06 GHz, v = 8.76 GHz and v = 17.0 GHz in a temperature range between 180 and 300 K.

Crystallography↗
PubMed1990

Residual motion of hemoglobin-bound spin labels and protein dynamics: viscosity dependence of the rotational correlation times.

The residual motion of spin labels bound to cysteine beta 93 and to lysines of methemoglobin has been studied by electron paramagnetic resonance spectroscopy. To separate the influences of the solvent and the protein environment of the label fluctuations, the correlation times, tau, were analyzed as a function of temperature for fixed solvent viscosities, eta. Results show that over a wide range of viscosity the dependence of tau on eta may be empirically described by a power law tau approximately eta kappa. The exponent kappa depends strongly on the location of the label on the protein surface. If one regards the spin labels as artificial amino acid side chains, characteristic values of correlation times and amplitudes of the rotational motion at the surface can be given. For eta = 1 cP and T = 297 K the correlation time of the labels bound to lysines is found to be tau = 9.10(-10) S and the rotational diffusion is nearly isotropic. The spin label bound to cysteine beta 93 occupies a protein pocket, its rotational motion is therefore restricted. The correlation time of the label motion within a limited motion cone of semi angle theta = 30 degrees +/- 3 degrees is found to be tau = 1.3.10(-9) S for eta = 1 cP and T = 297 K.

Animals↗
PubMed1989

Conformational transition of aquomethemoglobin: intramolecular histidine E7 binding reaction to the heme iron in the temperature range between 220 K and 295 K as seen by EPR and temperature-jump measurements.

Temperature-dependent EPR and temperature-jump measurements have been carried out, in order to examine the high-spin to low-spin transition of aquomethemogobin (pH 6.0). Relaxation rates and equilibrium constants could be determined as a function of temperature. As a reaction mechanism for the high-spin to low-spin transition, the binding of N epsilon of His E7 to the heme iron had been proposed; the same mechanism had been suggested for the ms-effect, found in temperature-jump experiments on aquomethemoglobin. A comparison of the thermodynamic quantities, deduced form the measurements in this paper, gives evidence that indeed the same reaction is investigated in both cases. Our results and most of the findings of earlier studies on the spin-state transitions of aquomethemoglobin, using susceptibility, optical, or EPR measurements, can be explained by the transition of methemoglobin with H2O as ligand (with high-spin state at all temperatures) and methemoglobin with ligand N epsilon of His E7 (with a low-spin ground state). Thermal fluctuations of large amplitude have to be postulated for the reaction to take place, so this reaction may be understood as a probe for the study of protein dynamics.

Animals↗
PubMed1989

[Correlation of the latency shift and brain stem potentials in basocochlear hearing loss and the time course of the click stimulus-induced evoked wave in the cochlea].

Frequency-specific information on high tone loss in the inner ear can, and if so only indirectly, be obtained from changes in latency of the click-evoked brain stem potential (ABR). The relationship between latency increases of the Jewett-wave-V in basocochlear hearing loss and the time course of the travelling wave on the basilar membrane will be presented. The latency increases of basocochlear hearing loss at 2 kHz, 1 kHz and 500 Hz correspond to both the computer-simulated time course of the travelling wave and to those of the derived responses. From a pathophysiological standpoint, receptor cells in basocochlear hearing loss are not functional, beginning at the oval window, so that, dependent on the degree of inactivity, a delay corresponding to that of the time course of the travelling wave passes until active hair cells are reached and action potentials released that produce, when summed up a potential of delayed latency.

Acoustic Stimulation↗
PubMed1988

Click ABR intensity-latency characteristics in diagnosing conductive and cochlear hearing losses.

A schematic description of the correlation between various pathologies of hearing impairments and the behavior of auditory brainstem responses (ABR) is presented. Conductive pathology and high-frequency cochlear hearing losses prolong wave component latency due to energy loss and hair cell dysfunction. In cases of flat cochlear hearing loss latency is not affected. Prolonged interwave latencies between wave I and wave V indicate eight nerve and brainstem disorders. An algorithm was developed in the form of a flow chart for locating various malfunctions. Fields of wave V intensity-latency functions were designed for the faster detection and more precise evaluation of conductive and cochlear hearing losses.

Algorithms↗
PubMed1988

A simple method for determination of rotational correlation times and separation of rotational and polarity effects from EPR spectra of spin-labeled biomolecules in a wide correlation time range.

A method using nitroxide radical spin labels for determining both the isotropic rotational correlation time tau R and the environmental polarity of the label is described. By means of a least square fitting method, the values of an effective hyperfine tensor A' and of an effective g value tensor g' of randomly oriented spin labels are determined from X-band EPR spectra on the basis of an effective time-independent Hamiltonian. The traces of the tensors deliver the information about the environmental polarity of the label and are not dependent on the rotational correlation time tau R. A new averaging parameter S (tau R), calculated on the basis of the principal values of the tensor A', permits the evaluation of the rotational correlation time tau R in a very wide time range between 10(-10) and 10(-6) s. An application of this method to spin-labeled methemoglobin over a large temperature range and in environments of different polarity is discussed.

Electron Spin Resonance Spectroscopy↗
PubMed1988

A continuous wave laser T-jump apparatus and its application to chemical reactions in hemoglobin single crystals.

A laser temperature jump apparatus is constructed where the T-jump is achieved by means of the direct absorption of continuous laser radiation of low intensity by a solid sample. The final temperature in the irradiated volume element is reached when the absorbed radiation power equals the dissipation of heat by heat conduction. The time range from the beginning of irradiation to the stationary state depends on the geometry of the irradiated volume element and is less than 10 ms. The heating laser beam is simultaneously used to detect the relaxation to the new chemical equilibrium in the sample. Relaxation processes with relaxation rates between 10(2) s-1 and less than 10(-3) s-1 on samples with volumes less than 10(-3) mm3 may be investigated using this T-jump method. One application of this method is the determination of reaction rates of ligand reactions in hemoglobin single crystals. Rate constants obtained for the reaction of thiocyanate with crystallized horse methemoglobin are presented.

Animals↗
PubMed1988

[Response latency characteristics for ENT medical assessment of auditory brain stem evoked response].

A schematic description of the correlation between the various types of hearing disorders and the behaviour of auditory brain stem responses (ABR) is presented. Conductive pathology and high-frequency cochlear hearing loss prolong wave component latency due to energy loss and hair cell dysfunction. Latency is not affected in flat cochlear hearing loss. Prolonged interwave latencies between wave I and wave V indicate eighth nerve and brain stem disorders. An algorithm in the form of a flow chart was developed for location of the malfunction. Families of characteristics of wave V intensity-latency functions were designed for faster detection and more precise evaluation of conductive and cochlear hearing losses.

Audiometry, Evoked Response↗
PubMed1988

[Effect of cochlear processes in generating Jewett IV and V brain stem potential components].

Polarity of the stimulus influences latency, amplitude and waveform of the human auditory brainstem response (ABR). One clear feature is the splitting of the wave complex JIV and JV in separate peaks following rarefaction stimulation. ABR was recorded using high-pass filtering to mask the basilar membrane partially to establish whether and to what extent basal hair cells contribute to waves IV and V. Wave IV disappeared in response to rarefaction stimuli with masking of the basal region. In contrast, wave V appeared with reduced amplitude and delayed latency in response to condensation stimuli. A model was developed to determine the motion of the basilar membrane and the distribution over time of the action potential on the auditory nerve fibers following rarefaction and condensation stimuli. The rarefaction stimulus produces a bifid and the condensation stimulus only a single-peaked contribution. It is suggested that the splitting of the wave complex IV and V may be traced to mechanical processing in the cochlea.

Auditory Pathways↗
PubMed1988

[Report of experiences (1974-1986) in classification and site distribution of malignant tumors of the organs of the inner nose and paranasal sinuses. A retrospective review of over 1,296 cases].

The 4th edition of the UICC classification of the TNM system came into force on 1st January 1987. New rules have been established for the classification of maxillary sinus tumors. We have compared these to the classification system used by the AO/HNO for all the sinuses and the nose. From a review of the world literature and analysis of 1296 patients registered in the years 1974 to 1986, it became clear that less than 60% of all malignant tumors of the nasal cavity and sinuses are primarily located in the maxillary sinuses. Furthermore, the primary site is often hard to define because of the high rate of T3 and T4 tumors (approx. 70%).

Humans↗
PubMed1987

[New and changed guidelines in the TNM system of head and neck tumors].

Starting on the 1st of January 1987, the 4th edition of the UICC classification of the TNM-system is to be applied. Only slight changes have been made in the rules for the larynx and the skin, whereas the classification of the nodal status has undergone a more profound change. New rules have been established for the classification of salivary gland and maxillary sinus tumours, including a stage grouping for the salivary glands. The R-classification is new and changes have been made in the histological grading. The head and neck part of the edition is presented. The classification for the maxillary sinuses is compared to a personal system covering all the sinuses and the nose: its usefulness has been proven by successful documentation of 1224 cases.

Head and Neck Neoplasms↗
PubMed1987

[Spatial representation of basilar membrane movement with 3D computer graphics].

A mathematical model of the cochlea was implemented on a computer. The basilar membrane motion was computed for single, two, and multi-tone stimuli as well as for musical sounds and vowels. The pattern of the travelling waves were presented in three-dimensional color computer graphics. The high performance 3D graphics system performs local hidden surface removal, 3D geometric transformations and supports local lighting models to generate truly realistic shading for complex 3D objects. An addressable 1280 by 1024 pixel matrix assures crisp, precise resolution of the finest detail in the graphic images. The spatial pattern of basilar membrane motion conveys an impression of the image of acoustic stimuli on the basilar membrane. Firstly, the motion pattern of the travelling wave to a single tone is presented. The superposition of several tones (two-tone, multi-tone) causes a superposition of the travelling waves along the basilar membrane whereby the place principle in the cochlear partition becomes more clearly recognizable. Sounds (flute and violin) and vowels (German "u" and "i") evoke a complex motion pattern on the basilar membrane. The realization of the chronological order of movements on the basilar membrane can be made by computer animation. This enables the analysis of the space-time patterns of complex acoustic stimuli.

Basilar Membrane↗
PubMed1985

[Instructions for the documentation of neoplasms in the area of the head and neck following the TNM system. Contribution to the validation of the TNM system].

As the only international classification scheme the TNM-system allows classification of practically all tumours of all organs according to uniform rules. In the interest of international comparison of findings and results the TNM-system alone can be recommended for classification. Checklists are used for extension of the basic documentation for the head and neck. Directions for initial and follow up analysis are given. The TNM-system in this proposed practice allows clear determination of the pre-therapeutic findings, recurrences to be taken into account, the course of the disease to be recorded, and the survival rate to be calculated. The data are suitable for recording on a computer. Finally uniform recommendations for treatment may be deduced.

Documentation↗
PubMedDate not supplied

Site directed spin labeling studies of structure and dynamics in bacteriorhodopsin.

Site-directed spin labeling of membrane proteins has been used to determine: (1) the topography of the polypeptide chain with respect to the membrane/solution interface, and (2) the identity and orientation of secondary structure in selected regions. These features are deduced from the collision rates of nitroxide side chains with paramagnetic reagents in solution, and the principles of the method are reviewed with reference to bacteriorhodopsin. The dynamics of the nitroxide side chains relative to the backbone reveal tertiary interactions of the labeled site, and provide a promising means of time-resolving conformational changes. This aspect is illustrated by recent studies of structural changes in bacteriorhodopsin during the photocycle. In these experiments, nitroxide side chains were introduced at residues 72, 101 and 105 after replacement of the original residues by cysteine. Upon flash photolysis, the electron paramagnetic resonance spectrum of a nitroxide at 101, but not those at 72 or 105, is time-dependent. The spectral change develops during the decay of the M-intermediate, and reverses upon return to the ground state. The results suggest a movement of the C-D or E-F interhelical loops during the protonation changes of aspartate 96.

Bacteriorhodopsins↗