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Biomedical subjects

D Schubert

Publications and source records attributed to D Schubert.

At least 145 records · Page 8Linked to original sources
PubMed1983

The binding of deoxycholic acid to band 3 protein from human erythrocyte membranes and to bovine serum albumin.

The binding of a water-soluble steroid, deoxycholic acid, to solubilized band 3 protein from erythrocyte membranes was studied by equilibrium dialysis. At acid pH, a single high affinity binding site with an association constant K = 4 . 10(5)M-1 was found. In addition, the protein showed a large number of low affinity binding sites. High affinity binding of the steroid was not observed when the pH was made alkaline or when deoxycholic acid was substituted by cholic acid. The results support the suggestion previously derived from monolayer experiments that band 3 possesses a single cholesterol-binding site of high affinity and specificity (Klappauf, E. & Schubert, D. (1979) Hoppe-Seyler's Z. Physiol. Chem. 360, 1225-1235). Bovine serum albumin was also found to possess a single high affinity binding site for deoxycholic acid (K = 4 . 10(5)M-1). In contrast to band 3, this site is observed both at acid and alkaline pH.

Animals↗
PubMed1983

The binding of Ca2+ to solubilized band 3 protein of the human erythrocyte membrane.

The binding of 45Ca2+ to isolated band 3 protein, the anion transport protein of the human erythrocyte membrane, was studied by equilibrium dialysis. The protein was solubilized and purified by either the nonionic detergent Ammonyx-L0 or acetic acid. Each preparation of band 3 protein showed a single high-affinity Ca2+ binding site and several Ca2+ binding sites of lower affinity. The association constant of the high-affinity site was 4-13 X 10(4)M-1; it was only moderately dependent on ionic strength. Mg2+ effectively competed with Ca2+ for the site. Anion exchange across the human erythrocyte membrane is inhibited by micromolar concentrations of intracellular Ca2+. Our results suggest that this inhibition is due to the binding of the cation to a single site on band 3 protein.

Anion Exchange Protein 1, Erythrocyte↗
PubMed1982

Band 3 protein-cholesterol interactions in erythrocyte membranes. Possible role in anion transport and dependency on membrane phospholipid.

Band 3 protein of the human erythrocyte membrane, the anion transport protein, possesses a high affinity steroid binding site. In mixed phospholipid-cholesterol monolayers, the state of occupancy of this site is positively correlated with their cholesterol and sphingomyelin content and negatively with their glycerophospholipid content. We suggest that, in the erythrocyte membrane, the binding site is an inhibitory site of anion transport and that the modulation of its state of occupancy by the membrane lipid is responsible for the negative correlation of anion transport with the membrane's content of cholesterol and sphingomyelin and the positive correlation with the phosphatidylcholine content.

Anion Exchange Protein 1, Erythrocyte↗
PubMed1982

The structure of mixed cholesterol-phospholipid monolayers spread at the air-water interface as probed by interactions with band 3 protein from erythrocyte membranes.

Solubilized band 3 protein from human erythrocyte membranes (the anion transport protein) interacts strongly and specifically with monolayers of cholesterol spread at the air-water interface whereas, at pH 7-10, it shows only moderate interactions with phospholipid monolayers (Klappauf, E. and Schubert, D. (1979) Hoppe-Seyler's Z. Physiol. Chem. 360, 1225-1235). When band 3 protein, at pH 7 and an ionic strength of approx. 100 mM, is added to the subphase of mixed cholesterol-glycerophospholipid monolayers, the changes delta pi in monolayer surface pressure induced by the protein depend on the mole fraction X of sterol in the mixture. However, delta pi (X) only increases with increasing X towards the high values of delta pi that are characteristic of cholesterol monolayers if X greater than 0.67 +/- 0.04; at lower cholesterol content, delta pi (X) is practically identical to the value obtained with the pure glycerophospholipid. With mixtures of coprostanol and glycerophospholipids, the break in the delta pi (X) curves occurs when X = 0.33 +/- 0.03. Cholesterol-sphingomyelin and epicoprostanol-phosphatidylethanolamine mixtures show an increase of delta pi (X) when X greater than 0. The data seem to support earlier claims that cholesterol can form stoichiometric complexes with glycerophospholipids, the stoichiometries revealed by the band 3-monolayer interactions being 2:1 and 1:2. They also show that cholesterol-sphingomyelin complexes, if they should exist, must be structurally different from the cholesterol-glycerophospholipid complexes.

Air↗
PubMed1982

Properties of extracellular adhesion-mediating particles in myoblast clone and its adhesion-deficient variant.

Both the skeletal muscle myoblast cell line L6 and an adhesion-deficient variant of L6 released glycoprotein complexes, termed adherons, into their culture medium. The adherons from the variant, M3A, differed from those of L6 in a number of properties. M3A adherons were much less effective in promoting the cell-substratum and cell-cell adhesion of myoblasts than L6 particles. The adherons from the two cell lines also differed in their relative sedimentation velocities in sucrose gradients and had different chemical compositions. The M3A particle lacked chondroitin and contained relatively less collagen and fibronectin than the L6 adheron. Both L6 and M3A particles adhered to plastic surfaces and cells equally well in the absence of calcium ions. Neither cell-cell adhesion nor particle aggregation occurred in calcium-free medium. However, in the presence of calcium, the L6 adherons aggregated completely and M3A particles aggregated poorly. These data suggest that at least two sets of interactions are required for adheron-mediated adhesion: a calcium-independent binding of the adheron to the cell, and a calcium-dependent interaction between particles that is directly responsible for adhesion. The M3A variant is blocked at the calcium-dependent step, resulting in an adhesion deficiency.

Calcium↗
PubMed1982

Alterations of lipid metabolism in response to nerve growth factor.

In response to nerve growth factor (NGF), clonal pheochromocytoma cells flatten and extend neurites capable of making functional synapses. Although no significant changes in overall phospholipid composition occur in the presence of NGF, there is increased incorporation of 32PO4 into phosphatidylinositol and phosphatidic acid within 10 min after the addition of NGF. NGF stimulates the incorporation of 32PO4 into other lipids, such as phosphatidylcholine, to a lesser extent. The kinetics of the NGF-induced phosphatidylinositol responses are different when the cells are in suspension from when they are attached to culture dishes. These changes in phospholipid metabolism are discussed with respect to their role in NGF-induced nerve differentiation.

Adrenal Gland Neoplasms↗
PubMed1982

The specificity of extracellular glycoprotein complexes in mediating cellular adhesion.

Complexes containing glycoproteins and glycosaminoglycans were released into the culture medium by both smooth and skeletal muscle cells. The particles, termed adherons, from three smooth muscle cell lines promoted cell-substratum adhesion of a clonal sympathetic nerve cell line, PC12. In contrast, the glycoprotein complexes from three skeletal muscle preparations inhibited the adhesion of PC12 cells to Petri dish surfaces. The skeletal muscle adherons all sedimented in calcium-free sucrose gradients with an S value of 16, while the smooth muscle particles had a sedimentation value of 12. Although both classes of adherons contained fibronectin and collagen, hyaluronic acid was present only in those from skeletal muscle. An antiserum prepared against skeletal muscle adherons blocked myoblast adhesion to skeletal muscle adherons but did not alter PC12 adhesion to smooth muscle adherons. These data suggest that the glycoprotein complexes released by muscle have some intrinsic specificity with respect to their ability to mediate cellular adhesion.

Animals↗
PubMed1981

The role of cAMP in the induction of ornithine decarboxylase by nerve and epidermal growth factors.

Nerve growth factor (NGF), epidermal growth factor (EGF), adenosine 3',5'-cyclic monophosphate (cAMP), and cholera toxin all increase the specific activity of ornithine decarboxylase (ODC) in the PC12 nerve-like cell line. A phosphodiesterase inhibitor augments the effect of NGF on the induction of ODC in these cells, while it is only additive with the EGF response. These data suggest that cAMP has an intermediary role in the induction of ODC by NGF and that cAMP is not involved in the EGF response.

Carboxy-Lyases↗
PubMed1980

Altered collagen and glycosaminoglycan secretion by a skeletal muscle myoblast variant.

A variant of the anchorage-dependent L6 skeletal muscle myoblast cell line which grows in suspension culture was selected. This cell line, designated M3A, is aneuploid and tumorigenic, while the parental L6 line is near diploid and nontumorigenic. L6 secretes high molecular weight collagen alpha-chains, and M3A secretes a collagen-like protein of Mr = 56,000, or approximately half the size of collagen alpha-chains. Finally, both L6 and M3A synthesize hyaluronic acid, heparan sulfate, chondroitin sulfate, and chondroitin. The latter glycosaminoglycan is not, however, released into the culture medium by M3A, nor is it found in the substrate-attached material synthesized by M3A. The changes in secreted and substrate-attached material synthesized by M3A are discussed in relation to its altered growth characteristics.

Amino Acids↗
PubMed1980

A role of secreted glycosaminoglycans in cell-substratum adhesion.

An adhesion-deficient variant, designated M3A, was derived from the anchorage-dependent L6 skeletal muscle myoblast line (Schubert, D., and La Corbiere, M. (1980) J. Biol. Chem. 255, 11557-11563). To investigate the defect in the M3A variant, adhesion to various substrata was studied. M3A adhered rapidly to substrate-attached material (SAM) prepared from L6 cultures and serum, but adhered slowly to SAM derived from M3A itself. The role of collagen and fibronectin in the adhesion of M3A cells to L6- and M3A-derived SAMs was ruled out, but several experiments suggested that glycosaminoglycans play a rate-limiting role in the adhesion process. The adhesive interaction of the M3A cells with the different substrata is specific with respect to the glycosaminoglycans involved, since the type and concentration of purified glycosaminoglycans required to inhibit the interaction is unique to each surface. An alteration in glycosaminoglycan synthesis by M3A cells may account for the difference in the adhesive properties of SAM derived from L6 and from the M3A variant.

Animals↗
PubMed1980

The modulation of neurotransmitter synthesis by steroid hormones and insulin.

Glucocorticoids stimulate tyrosine hydroxylase activity and catecholamine synthesis, while markedly inhibiting acetylcholine synthesis and storage in the a clone of sympathetic nerve-like cells. Nerve growth factor enhances the effect of glucocorticoids on tyrosine hydroxylase. The steroid effect is specific for glucocorticoids, since 11-desoxycortisol, testosterone, and estradiol-17 beta do not reproduce the effects of hydrocortisone and dexamethasone. Concomitant with the shift in neurotransmitter synthesis, there is an increase in the mean diameter of intracellular dense core vesicles. In contrast to glucocorticoids, insulin increases the specific activity of choline acetyltransferase through the interaction with typical insulin receptors. Insulin does not, however, alter the morphology of the cells, nor does it block the morphological response of the cells to nerve growth factor.

Acetylcholine↗
PubMed1980

Role of a 16S glycoprotein complex in cellular adhesion.

Myogenic cells release into their culture medium a glycoprotein complex that mediates cellular adhesion. In the absence of calcium this complex has a sedimentation value of 16S; it aggregates in the presence of calcium. The 16S material both agglutinates and increases the rate of cell-substratum adhesion of a myoblast variant and inhibits the adhesion of a nerve-like cell line to culture dishes. It is also a hemagglutinin. The 16S particle is composed of glycosaminoglycans and several proteins, including fibronectin and collagen.

Animals↗
PubMed1980

Interactions of band 3-protein from human erythrocyte membranes with phospholipid monolayers at the air-water interface.

Lipid monolayers at the air-water interface were used as a model system to study the interactions of solubilized band 3-protein of the human erythrocyte membrane with phospholipids. The changes in monolayer surface pressure accompanying protein incorporation were used as a measure of the strength of the protein-lipid interactions. The following results were obtained: (1) Both polar and apolar forces contribute to the protein-lipid interactions, the latter being predominant. (2) The interactions strongly depend on the pH of the monolayer subphase. They are much stronger at acid than at neutral or alkaline pH. (3) The influence of pH on the band 3-phospholipid interactions is mainly due to a pH-induced conformational change of the protein, the pK value of which is near 5.0. (4) At all pH values studied, band 3 shows the highest affinity for phosphatidic acid and phosphatidylglycerol, the lowest for sphingomyelin and phosphatidylcholine.

Air↗