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Biomedical subjects

H Richter

Publications and source records attributed to H Richter.

At least 163 records · Page 9Linked to original sources
PubMed1983

Localization of the chemotactic domain in fibronectin.

Fragments derived from human plasma fibronectin by enzymatic degradation were tested in the Boyden chamber for chemotactic activity towards various fibroblast strains. The results provide clear evidence that the chemotactic activity is restricted to a defined region of the fibronectin molecule which is the same for various fibroblast strains. The active domain is localized between the collagen binding site and the major heparin binding site, about 170 kDa apart from the N-terminal and about 70 kDa from the C-terminal ends of the two subunit peptide chains.

Binding Sites↗
PubMed1983

A large cathepsin D-derived fragment from the central part of the fibronectin subunit chains.

A mild cathepsin D digest of fibronectin only contained single-chain peptides of 200, 140 and 70 kDa and double-chain fragments of about 300 and 140 kDa containing the C-terminal disulfide link. Among the single-chain fragments the 200 kDa peptide was a precursor of the 140 kDa and 70 kDa peptides. The latter was correlated to the N-terminal and the former to the central region of the fibronectin subunit chains.

Cathepsin D↗
PubMed1983

Discrimination of different domains in fibronectin on the basis of their stability against urea denaturation.

Circular dichroism spectra, thermal transition profiles and proteolytic susceptibility showed that different regions in the multidomain protein fibronectin exhibit different sensitivity against urea denaturation. A 70-kDa fragment obtained by cathepsin D treatment which comprises the N-terminal part of the fibronectin chains, exhibited in 8M urea a spectrum, at 20 degrees C, identical to that of the native fragment and its thermal unfolding was shifted to lower temperatures by only 10 degrees C. The central portions of the fibronectin chains were remarkably unfolded under the same conditions as clearly demonstrated by the spectra and transition profiles of a cathepsin D-raised 125/140-kDa fragment which originates from this region. When fibronectin or its fragments were exposed to 4 or 8M urea at 4 degrees C and the urea subsequently dialysed off, the spectra and transition curves recorded were very similar to those of the native proteins. Nevertheless, this treatment introduced local conformational changes which resulted in the creation of three new cleavage sites for chymotrypsin. The most prominent one was found to be located in the central part of the middle region and no sites were created in the N-terminal 70-kDa region. In the conjunction with sequence information [Petersen et al. (1983) Proc. Natl. Acad. Sci. USA 80, 137-141] it may be concluded that the disulfide rich domains, made up by regions of internal homology of types I and II in the N-terminal portion of fibronectin, exhibit a remarkable conformational stability, whereas the disulfide free middle region which contains type III domains, is much less stable. Some domains in this region are particularly sensitive to urea denaturation and are irreversibly affected already by 4M urea at 4 degrees C. Therefore, the use of high urea concentrations for the elution of fibronectin from affinity columns may lead to an at least partially irreversible unfolding of some domains and a loss of functions associated with these structural elements.

Chymotrypsin↗
PubMed1983

Generation of fibronectin receptors on macrophages by wheat germ lectin.

A chymotrypsin-derived and 125I-labelled 125-kDa fragment of human plasma fibronectin which contained the cell binding site, was only weakly bound by peritoneal macrophages of guinea pigs and binding was not saturable. In presence of wheat germ lectin binding increased proportionally to the logarithm of the lectin concentration. Association of 125I-fragment with cells was partially prevented by non-labelled fragment indicating a saturable receptor-ligand interaction. An apparent affinity constant of about 2--4 x 10(-5) M was evaluated. A considerable fraction of the cell-bound 125I-fragment resisted removal by proteases suggesting that it was internalized. In order to investigate an influence of wheat germ lectin on the binding of 125I-fibronectin by the cells the macrophages were preincubated with the lectin followed by washing and evaluation of 125I-fibronectin binding. A simultaneous incubation of the cells with 125I-fibronectin and lectin was impractical due to partial interaction of the two proteins giving rise to some unspecific precipitates. Preincubation with wheat germ lectin considerably improved the capacity of the macrophages for binding of 125I-fibronectin. Again the binding of 125I-labelled protein could be restricted by unlabelled one. N-acetyl-glucosamine inhibited the binding of 125I-fibronectin by wheat germ lectin-treated cells if applied in the preincubation phase and more effectively, if applied in the final 125I-fibronectin binding assay. N-Acetylneuraminic acid also inhibited this step. In addition to wheat germ lectin concanavalin A was capable of generating fibronectin receptors on the cell surface. Soy bean lectin, however, was ineffective.

Animals↗
PubMed1983

Shape and stability of fibronectin in solutions of different pH and ionic strength.

At low ionic strength (0.05 M) the sedimentation coefficient of monomeric plasma fibronectin was found to vary from 8S, at pH 3 and 11, to 13.5S at neutral pH. The lower s20,w value indicates a stretched arrangement of the value indicates a stretched arrangement of the two arms of the molecule which was observed in most electron microscopic studies. The higher value is consistent with a still very asymmetric but more condensed shape, which is probably brought about by back-folding and interactions between chain segments of different net charge. A model of this internal association is based on the finding that segments of rather different isoelectric points alternate along the fibronectin chains. A similar pH dependence was observed for a 140-kDa fragment from the middle region of fibronectin which carries segments of low and high isoelectric points at its ends. At high ionic strength (0.35 M) the pH dependence of the sedimentation coefficients was less pronounced and intermediate s20,w values were found. This is expected when both repulsive and attractive interactions are weakened by the electrolyte. It was verified by circular dichroism spectra that the protein was not denatured at pH 3 or 11. Thermal transition curves revealed a destabilization at pH 3 but the thermal denaturation occurred well above 20 degrees C at which the pH dependence of the solution shape was studied.

Drug Stability↗
PubMed1983

[Determination of left ventricular volumes using 2-dimensional echocardiography in children].

In the first part of the study we examined silicone rubber left ventricular casts of children and adolescents by cross-sectional echocardiography using the so-called two-chamber and four-chamber apical views. Left ventricular volumes calculated from the echocardiographic left ventricular silhouettes correlated very well (r = 0.99) with the titrated cast volumes. In the second part of the study we compared in 30 infants, children, and adolescents left ventricular volumes as calculated from the two-chamber and four-chamber apical echocardiographic views with those obtained from the frontal projection of the left ventricular cineangiogram. Volumes calculated from the apical four-chamber view showed an acceptable correlation with those determined by angiography (r = 0.96 for enddiastolic and r = 0.90 for endsystolic volume). Underestimation of left ventricular enddiastolic volume by echocardiography was corrected by a factor of 1.33; no correction factor was necessary for the endsystolic volume. The correlation between the endsystolic volumes obtained by echocardiographic two-chamber view and by cineangiography was poor. Finally, in 51 infants, children, and adolescents without heart disease we determined left ventricular volumes and derived variables by cross-sectional echocardiography, using the previously established correction factor for the calculation of enddiastolic volumes. Both enddiastolic and endsystolic volumes were found to correlate linearly to body surface area.

Adolescent↗
PubMed1982

Failure of ceramic hip endoprostheses by slow crack growth--lifetime prediction.

The slow crack propagation velocity v, which depends on the stress intensity factor K, has been measured for three different high-density aluminas. Assuming a load history for the prosthesis which approximates conditions during walking, the lifetimes of the components of a total hip endoprosthesis were calculated as a function of the initial flaw size. Different geometries for the preexisting cracks, as well as varying physiological parameters, were considered. It is shown that the lifetime is very dependent on the quality of the material and that it is reduced by increased body weight, walking speed, and varus positioning. Comparison of failure behavior in different parts of the femoral component showed that flaws in the stem must be one order of magnitude smaller than those in the neck to achieve comparable lifetimes.

Body Weight↗
PubMed1982

Central control of peripheral circulating somatostatin in dogs: effect of 2-deoxyglucose.

Circulating plasma somatostatin concentrations are known to fluctuate in response to nutrients and hormones. However, little is known about neural or central nervous system (CNS) control of somatostatin secretion. To test whether peripheral circulating somatostatin is influenced by a central stimulus, 2-deoxyglucose (37.5 mg/kg) was infused into a lateral cerebral ventricle of six conscious dogs over a period of 15 min. Plasma somatostatin levels rose from a base line of 105 +/- 6 pg/ml (mean +/- SE) to a peak of 154 +/- 10 pg/ml (P less than 0.005) at 30 min after the onset of the infusion. Somatostatin levels were still significantly elevated (P less than 0.025) at 60 min (119 +/- 6 pg/ml) and thereafter gradually returned toward base line. Plasma glucose and glucagon levels increased in response to intraventricular 2-deoxyglucose. Glucose concentrations rose from 105 +/- 5 mg/dl to peak at 203 +/- 16 mg/dl (P less than 0.005) at 80 min and remained elevated to 120 min. The concentration of plasma glucagon increased from 41 +/- 6 to 92 +/- 18 pg/ml at 60 min (P less than 0.05) and then declined. In marked contrast to intraventricular 2-deoxyglucose, similar concentrations of 2-deoxyglucose administered intravenously (n = 4) resulted in a slight fall in plasma somatostatin. Intraventricular saline did not result in a change in plasma somatostatin. It is concluded that peripheral circulating somatostatin may be susceptible to central nervous system control.

Animals↗