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Biomedical subjects

K Eckert

Publications and source records attributed to K Eckert.

At least 55 records · Page 3Linked to original sources
PubMed1992

A new monoclonal antibody for detection of EGF-receptors in western blots and paraffin-embedded tissue sections.

The prognostic significance of the epidermal growth factor receptor status (EGF-R-status) for certain human tumors requires the development of antibodies useful for clinical application. We used purified receptor preparations to generate monoclonal antibodies immunoreactive with the EGF-R purified from placenta membranes and A431 tumors. Four of the hybridomas contained antibodies (R2, R3, R5, and R9) which recognized both antigens. Antibody R3 was shown to display the following properties: it binds with a KD value of about 10(-9)-10(-10) M to the receptor, a half maximal inhibition of EGF-binding is achieved at 5 x 10(-8) M, and in Western blots of cell membranes R3 specifically detects the EGF-R at 0.1 micrograms/ml. R3 inhibits EGF-dependent clonogenic growth of NRK cells and completely blocks EGF stimulated autophosphorylation of the receptor. Moreover, R3 also detects EGF-R in paraffin-embedded tissue sections taken from human salivary gland, term placenta, and adult skin and mammary carcinomas. Thus, R3 can be used in retrospective diagnostic clinical studies and might help to develop new immunotherapeutic intervention.

Animals↗
PubMed1990

A Mr 43,000 epidermal growth factor-related protein purified from the urine of breast cancer patients.

A tumor-associated epidermal growth factor (EGF)-like activity was detected in the urine of breast cancer patients by means of an EGF radioreceptor assay and an anchorage-independent growth assay. The clonogenic growth factor activity of pooled void volume eluate fractions from a Bio-Gel P-30 column was completely neutralized by an anti-human epidermal growth factor antiserum but not by an anti-transforming growth factor alpha antiserum. This activity was determined in the urine of 71 breast cancer patients. A statistically significant correlation was found between EGF-like clonogenic activity and axillary lymph node status, tumor size, stage of disease, and grade of differentiation of the primary tumor. The Bio-Gel P-30 void volume fraction was used to purify the EGF-related polypeptide to apparent homogeneity by subsequent binding to and elution from A431 cells followed by isoelectric focusing. A polypeptide of a pI of approximately 3.4 was identified to be related to EGF by neutralization and immunoprecipitation experiments with anti-human epidermal growth factor antisera. This polypeptide migrated as a single band of Mr 43,000 in sodium dodecyl sulfate-polyacrylamide gel electrophoresis.

Biological Assay↗
PubMed1989

Purification of a high molecular weight form of epidermal growth factor from urine of breast cancer patients.

A high molecular weight form of epidermal growth factor (EGF) was detected by means of an EGF radio-receptor assay and an anchorage-independent growth assay in the urine of breast cancer patients. Preliminary data indicate that the activity of this growth factor is associated with lymph node status and tumor size and that the activity becomes reduced after removal of the primary tumor. The EGF-related polypeptide was purified to homogeneity by a combination of Sephadex G-25 and Bio Gel P-30 chromatography followed by binding to, and elution from, EGF receptor rich A431 cells. Final purification was achieved after isoelectric focusing by following the biological activity of eluted polypeptides. A polypeptide of a pI of 3.4 was identified to carry EGF-like activity. This polypeptide migrated as a single band of 43 kDa in SDS-PAGE. Its biological activity was neutralized by a specific anti-hEGF-antibody indicating an immunological relationship with hEGF.

Animals↗
PubMed1988

Effects of anti-EGF serum on newborn mice.

Administration of anti-EGF serum to newborn mice led to delay of eyelid opening and incisor tooth eruption, acceleration of hair growth and delay of weight gain. These results indicate that in the first week after birth EGF still has a physiological function, which can be abrogated by anti-EGF serum.

Animals↗
PubMed1985

Secretion of phosphoproteins associated with neoplastic transformation and with the action of transforming growth factors.

Incubation of conditioned media derived from mammary epithelial cells and from fibroblasts with [gamma-32P]ATP revealed much higher intensities of labeled polypeptides in transformed cells compared to normal cells. Conditioned media from human mammary carcinoma cells have in common the presence of characteristic phosphoproteins with molecular masses of about 37,22 and 19.5 kDa. Ehrlich Ascites Mammary Carcinoma Cells secrete a dominant 32 kDa phosphoprotein. Normal fibroblasts secrete elevated levels of phosphoproteins after treatment with transforming growth factors. A phosphoprotein with molecular mass of about 37 kDa becomes secreted preferentially if cell-conditioned media were labeled in vivo. The results indicate that the phosphoproteins comprise a family of secretory polypeptides associated with early steps of transformation.

Animals↗
PubMed1985

Demonstration of transforming growth factor activity in mammary epithelial tissues.

Transforming growth factor (TGF) activity has been demonstrated in acid-ethanol extracts of bovine mammary gland, of Ehrlich Ascites Mammary Carcinoma Cells, and of the ascites fluid. The extracts differ in their activity in the soft agar test when using either human or rat fibroblasts. The most active extract obtained from mammary gland tissue was chromatographed and the TGF activity shown to be coeluting with EGF receptor-competing activity. The present data and our previous reports show that TGFs and a growth inhibitor for mammary epithelial cells coexist in bovine mammary gland as separate growth factors.

Animals↗
PubMed1982

Incorporation of Na+ - Ca2+ antiporter and of (Na+ + K+)-ATPase into liposomes and demonstration of their non-identity.

(Na+ + K+)-ATPase was isolated from the grey matter of brain and incorporated into liposomes. Most of the reconstituted enzyme was oriented 'inside-out' with respect to its in vivo orientation and externally added ATP promoted Na+ uptake that was inhibitable by internally trapped ouabain. Using the same proteoliposomes, an Na+ - Ca2+ exchange system was observed as indicated by the following pieces of evidence. (1) The Na+ gradient provided the only readily apparent driving force for acceleration of Ca2+ accumulation into proteoliposomes. (2) The antiporter was specific for Ca2+, high Mg2+ excess did not inhibit Ca2+ antiport. (3) The Na+ efflux was dependent on the extravesicular Ca2+ concentration. (4) The Na+ efflux was not inhibited by tetrodotoxin. The demonstrated Na+ - Ca2+ exchange could not be related to (Na+ + K+)-ATPase protein, since it was not purified with (Na+ + K+)-ATPase, as followed from transport studies with liposomes containing (Na+ + K+)-ATPase of different specific activity. The results strongly indicate that plasma membranes isolated from the grey matter of brain contain an Na+ - Ca2+ exchange system and that the proteoliposomes are suitable for further purification of the carrier molecule.

Animals↗
PubMed1978

Analysis of function-related interactions of ATP, sodium and potassium ions with Na+- and K+-transporting ATPase studied with a thiol reagent as tool.

The paper describes the interaction of ATP, Na+ and K+ with (NaK)-ATPase exploiting the inactivation by reaction with NBD-chloride as an analytical tool for the evaluation of enzyme ligandation with the various effectors. 1. The inactivation of (NaK)-ATPase by reaction with NBD-chloride showing under all conditions studied a pseudo first-order rate rests on the alkylation of thiol groups in or near catalytic centre. ATP bound to catalytic centre prevents from enzyme inactivation by NDD-chloride through protection of these thiol groups from alkylation. Na+ and K+ affect the reactivity of the thiol groups towards NBD-chloride either indirectly via influencing ATP binding or more directly via changing the conformation of catalytic centre. Proceeding from these interrelations, the interaction of the various effectors with the enzyme was analyzed. 2. The K'D-values of various nucleotides determined by our approach correspond to the values obtained by independent methods. As shown for the first time, two catalytic centres per enzyme molecule exist. They exhibit high or low affinity to both ATP and ADP apparently caused by anticooperative interaction of the half-units of the enzyme through intersubunit communication ("half-of-the-sites reactivity"). 3. In the absence of ATP, Na+ or K+ ligandation of (NaK)-ATPase produce opposite effects on the reactivity of the thiol groups of catalytic centres reflecting different changes of their conformation. This corresponds to the well-known antagonistic effect of Na+ and K+ on some partial reactions of (NaK)-ATPase. The Na+ and K+ concentrations required to change thiol reactivity are rather high, i.e. the ionophoric centres for both Na+ and K+ are not readily accessible for cation complexation in the absence of enzyme complexation with ATP. 4. Na+ being without effect on ATP binding to the enzyme also does not influence the inactivating reaction with NBD-chloride while K+ by decreasing ATP binding dramatically decreases the protective effect of ATP. The K+ affinity of the enzyme-ATP complex is by more than two orders of magnitude higher than that of free enzyme. Na+ ligandation of the K+-liganded enzyme-ATP complex reverses the effect of K+ ligandation and produces a protective effect which distinctly surpasses that of the complexation of free enzyme with ATP. Hence, the enzyme molecule carries simultaneously ionophoric centres for both Na+ and K+. 5. The findings that per enzyme molecule ionophoric centres for Na+ and K+, and two catalytic centres with anticooperative interaction coexist corroborate the corresponding basic predictions of the flip-flop concept of (NaK)-ATPase pump mechanism, and explain some peculiar kinetic features of transport and enzyme activities of (NaK)-ATPase.

4-Chloro-7-nitrobenzofurazan↗
PubMed1977

Spectroscopic studies on effector-induced and substrate-induced conformation changes of phosphofructokinase.

The interaction of phosphofructokinase with NH4+, AMP, ATP, citrate, MgATP or fructose 6-phosphate, and in part with their mixtures forming either binary or ternary complexes has been studied by means of ultraviolet difference spectroscopy and circular dichroism spectroscopy in the wavelength range 265-300 nm with the aim of characterizing the conformational corollaries of the ligand effects on phosphofructokinase. The positive as well as the negative effectors change phosphofructokinase conformation in different ways, not easily interpretable in terms of one active and one inactive enzyme conformation. The spectroscopic equivalents of phosphofructokinase conformation changes resulting from catalytic activity are similar to those produced by the reaction products. The ligand concentration-dependent changes of absorption differences in the tryptophyl, tyrosyl and phenylalanyl region parallel each other, i.e. the interactions of the ligands with phosphofructokinase are not confined to specific aromatic side chains, but involve conformation changes of the large domains of the protein. ATP affinity to the enzyme shows temperature-dependent biphasic changes so that ATP binding appears to be either an entropy-driven or enthalpy-driven process. The dissociation constants of the ligands derived from spectroscopic titration of binary complex formation are comparable to those calculated from kinetic experiments. MgATP and fructose 6-phosphate each alone change phosphofructokinase conformation by binary complex formation in keeping with a random order of reaction sequence.

Adenosine Monophosphate↗
PubMed1977

Determination and functional significance of low affinity nucleotide sites of Ca2+ + Mg2+ -dependent ATPase of sarcoplasmic reticulum.

The protective effect of ATP, ADP and GTP against the inactivation of Ca2+ + Mg2+ -dependent ATPase by the thiol reagent NBD-chloride is used to calculate the apparent dissociation constants (K'D) of nucleotide enzyme complexes on the basis of a simple kinetic model. The K'D-values of the complexes with Mg-ATP (80 micrometer) and Mg-GTP (500 micrometer) are found to be rather close to their Km-values in the high concentration range supporting maximum activity. The requirement of the occupancy of the low affinity site by Mg ATP for a high rate of the Ca2+ transport system is explained in terms of the flip-flop mechanism established earlier for the analogous Na+ + K+-transporting ATPase system.

4-Chloro-7-nitrobenzofurazan↗
PubMed1975

On the influence of fructose-6-phosphate, ammonium, ATP and AMP on the conformation of the phosphofructokinase from rabbit muscle.

By means of circular dichroism measurements in the range from 210-240 nm and 250-300 nm it is shown that conformational changes of the phosphofructokinase from rabbit muscle correlate with the action of effectors on the enzyme. The postulated active and inactive states differ in the secondary structure. Addition of activators causes a conformational change which is interpreted as the transition of the inactive into the active state. At 210-240 nm no reversion could be observed but at 250-300 nm there are some indications for at least partial reversion.

Adenosine Triphosphate↗