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Biomedical subjects

F Spener

Publications and source records attributed to F Spener.

At least 91 records · Page 5Linked to original sources
PubMed1995

Development of a heterogeneous amperometric immunosensor for the determination of apolipoprotein E in serum.

Apolipoprotein (apo) E is a constituent of serum lipoproteins and can serve as a diagnostic parameter for the assessment of disorders of lipid metabolism. For the determination of apo E in serum a sandwich-type amperometric immunosensor using disposable membranes was developed. The best results were obtained by using a site-directed attachment of a monoclonal capture antibody to a hydrazide-functionalized membrane surface. Bound antigen was then determined with the aid of a polyclonal antibody labelled with alkaline phosphatase in conjunction with p-aminophenyl phosphate as substrate. In this approach a carbon working electrode (vs. Hg/HgCl2) was used, and enzymatically generated p-aminophenol could be monitored with a detection limit of 40 pmol and a linear range of 26-20000 nM. The sensor displayed a linear response from 50 to 1000 ng ml-1 apo E. In contrast, antibody coupling through primary amino groups led to a total loss of antigen binding capacity in this assay configuration. The approach with site-directed immobilization however, not only allowed the determination of apo E in serum, but also the determination of antibody cross-reactivity against the apolipoproteins AI, AII and B.

Aminophenols↗
PubMed1994

Decrease and increase of responses to glutamate receptor agonists in RNA-injected Xenopus oocytes by the epileptogenic agent pentylenetetrazol: dependence on the agonist concentration.

The effects of the epileptogenic agent pentylenetetrazol (PTZ) on current responses to glutamate (Glu) and to the Glu receptor agonist N-methyl-D-aspartate (NMDA), kainate (KA), alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) and quisqualate (QA) were studied on RNA-injected Xenopus oocytes. PTZ antagonized the reactions to Glu as well as to NMDA, KA, AMPA and QA. With increasing concentration of AMPA, however, the depressive effect of PTZ turned to an augmentation. The complete change from a decreasing to an increasing effect of PTZ with elevated agonist concentration was unique for current responses by AMPA.

Animals↗
PubMed1994

N-terminal variants of fatty acid-binding protein from bovine heart overexpressed in Escherichia coli.

An expression vector for bovine heart fatty acid-binding protein (H-FABP) was constructed by introducing the coding part of the cDNA into the pET-3d vector. Transformed Escherichia coli strain BL21 (DE3)pLysS produced functional recombinant H-FABP up to 40% of the soluble proteins. The expression of fatty acid-binding protein was under the control of the T7-phi 10 promoter and the corresponding T7-RNA-polymerase in turn was induced by isopropyl beta-D-thiogalactopyranoside. By combination of cation exchange chromatography and gel filtration pure recombinant protein was obtained exhibiting isoelectric heterogeneity. Recombinant H-FABP was resolved into at least six variants with isoelectric points between 5.1 and 5.6. After separation by preparative isoelectric focusing the four major variants were digested with trypsin and the resulting peptides were characterized by high performance liquid chromatography (HPLC), matrix assisted laser desorption/ionization (MALDI) mass spectrometry, amino acid sequencing and chemical modification. The structural differences were traced back to the N-termini beginning with either methionine, as expected from the cDNA, or methionine sulfoxide, valine and N-formyl methionine. The latter three arise from oxidation, cleavage of N-terminal methionine and incomplete deformylation, respectively.

Animals↗
PubMed1994

Differentiational regulation and phosphorylation of the fatty acid-binding protein from rat mammary epithelial cells.

From the soluble protein fraction of lactating rat mammary epithelial cells, fatty acid-binding protein (FABP) was isolated by immunoaffinity chromatography. After digestion with trypsin, peptides were characterized with time-of-flight mass spectrometry and revealed identity with corresponding peptides derived from the heart-type FABP isolated from rat heart. In addition, by electrospray mass spectrometry the molecular mass has been determined to 14683.9 +/- 3 Da, further corroborating the identity. The content of FABP in mammary glands from virgin, pregnant and lactating rats was evaluated using two-dimensional gel electrophoresis and a FABP-specific immunosorbent assay. In the two-dimensional gels FABP was the apparently most abundant cytosolic protein in mammary epithelial cells from rats in late pregnancy as well as from lactating rats. The content of FABP was 59 +/- 19 microgram/mg (n = 11) of soluble proteins from the fully differentiated lactating mammary gland as determined by ELISA. This value represented an 80-fold increase compared with the FABP content of mammary gland from virgin rats, and is comparable with the level found in rat heart. Upon stimulation with insulin a small fraction of FABP was phosphorylated in lactating mammary epithelial cells. In conclusion, these findings indicate that the FABPs from rat mammary gland and heart are identical and further suggest that in mammary gland this FABP may play a role in signal transduction downstream from the insulin receptor.

Amino Acid Sequence↗
PubMed1994

Crystallization and preliminary X-ray analysis of a lipase from Chromobacterium viscosum.

Lipase from Chromobacterium viscosum has been purified to homogeneity and crystallized in a form suitable for X-ray diffraction analysis from 10-14% polyethylene glycol 4000 and 10-14% 2-methyl-2,4-pentane diol at pH 6.4 in the presence of 0.25%(w/v) n-octyl-beta-D-glucopyranoside. These crystals belong to space group P2(1)2(1)2 with refined lattice constants a = 41.1 A, b= 156.8, c = 43.6 A, indicating a cell content of one monomer per asymmetric unit of the crystal. The crystals diffract to a resolution of 2.2 A.

Journal Article↗
PubMed1994

Members of the fatty acid binding protein family are differentiation factors for the mammary gland.

Mammary gland development is controlled by systemic hormones and by growth factors that might complement or mediate hormonal action. Peptides that locally signal growth cessation and stimulate differentiation of the developing epithelium have not been described. Here, we report that recombinant and wild-type forms of mammary-derived growth inhibitor (MDGI) and heart-fatty acid binding protein (FABP), which belong to the FABP family, specifically inhibit growth of normal mouse mammary epithelial cells (MEC), while growth of stromal cells is not suppressed. In mammary gland organ culture, inhibition of ductal growth is associated with the appearance of bulbous alveolar end buds and formation of fully developed lobuloalveolar structures. In parallel, MDGI stimulates its own expression and promotes milk protein synthesis. Selective inhibition of endogenous MDGI expression in MEC by antisense phosphorothioate oligonucleotides suppresses appearance of alveolar end buds and lowers the beta-casein level in organ cultures. Furthermore, MDGI suppresses the mitogenic effects of epidermal growth factor, and epidermal growth factor antagonizes the activities of MDGI. Finally, the regulatory properties of MDGI can be fully mimicked by an 11-amino acid sequence, represented in the COOH terminus of MDGI and a subfamily of structurally related FABPs. This peptide does not bind fatty acids. To our knowledge, this is the first report about a growth inhibitor promoting mammary gland differentiation.

Amino Acid Sequence↗
PubMed1994

The expression pattern of a novel gene encoding brain-fatty acid binding protein correlates with neuronal and glial cell development.

Fatty acid binding proteins (FABPs) are a multigene family of small intracellular proteins that bind hydrophobic ligands. In this report we describe the cloning and expression pattern of a novel member of this gene family that is specifically expressed in the developing and adult nervous system and thus was designated brain (B)-FABP. B-FABP is closely related to heart (H)-FABP with 67% amino acid identity. B-FABP expression was first detected at mouse embryonic day 10 in neuroepithelial cells and its pattern correlates with early neuronal differentiation. Upon further development, B-FABP was confined to radial glial cells and immature astrocytes. B-FABP mRNA and protein were found in glial cells of the peripheral nervous system such as satellite cells of spinal and cranial ganglia and ensheathing cells of the olfactory nerve layer from as early as embryonic day 11 until adulthood. In the adult mouse brain, B-FABP was found in the glia limitans, in radial glial cells of the hippocampal dentate gyrus and Bergman glial cells. These findings suggest a function of B-FABP during neurogenesis or neuronal migration in the developing nervous system. The partially overlapping expression pattern with that of cellular retinoid binding proteins suggests that B-FABP is involved in the metabolism of a so far unknown hydrophobic ligand with potential morphogenic activity during CNS development.

Amino Acid Sequence↗
PubMed1993

Amino acid exchange and covalent modification by cysteine and glutathione explain isoforms of fatty acid-binding protein occurring in bovine liver.

A unique property of the liver-type member of the family of fatty acid-binding proteins is the heterogeneic pattern observed upon isolation, which can only partly be ascribed to the state of lipidation. Here we unraveled the structural basis of the heterogeneity of delipidated liver-type fatty acid-binding protein (L-FABP). Charge fractions of L-FABP focusing at pH 6.0 and at pH 7.0/7.1 were first isolated from bovine liver. Upon reduction, however, two distinct isoforms, namely pI 6.0 L-FABP and pI 7.0 L-FABP, were observed. From these isoforms peptides were generated enzymically and chemically by four independent methods. Peptides were separated by reverse phase high performance liquid chromatography and analyzed by Edman degradation and plasma desorption mass spectrometry. The complete amino acid sequences of the isoforms were established; they consist of 127 amino acids and each is N-terminally blocked with an acetyl group. The difference between pI 6.0 L-FABP and pI 7.0 L-FABP was attributed to an asparagine-aspartate exchange at position 105. When tryptic peptides of the pH 7.0/7.1 fraction were analyzed, discrepancies between sequence and mass data of the peptides containing at position 69 the sole cysteine of L-FABP led to the disclosure of a cysteinylation occurring at this position and giving rise to the slightly more basic pH 7.1 species. Moreover, chemical modification studies revealed that a part of the pH 6.0 fraction was pI 7.0 L-FABP that was glutathionylated at Cys69. Neither modification, however, prevented the binding of fatty acids. Together amino acid exchange and covalent modification of cysteine entirely explain the heterogeneity of L-FABP from bovine liver.

Amino Acid Sequence↗
PubMed1993

Isoforms of fatty-acid-binding protein in bovine heart are coded by distinct mRNA.

In the course of our studies on structure/function relationships of fatty-acid-binding proteins, we reported earlier that the two isoforms of the 15-kDa cardiac fatty-acid-binding protein (cFABP) from bovine heart only differ in one position; Asn98 in pI 5.1-cFABP; Asp98 in pI 4.9-cFABP [Unterberg, C., Börchers, T., Højrup, P., Knudsen, J. and Spener, F. (1990) J. Biol. Chem. 265, 16,255-16,261]. In the present study, we elucidate the origin for this heterogeneity. Isoelectric focusing analysis of immunoprecipitated in vitro translation products from total mRNA and positive-hybrid-selected cFABP/mRNA revealed two L-[35S]methionine-labeled proteins corresponding to pI 5.1-cFABP and pI 4.9-cFABP. In a control experiment, recombinant mRNA derived from cDNA encoding pI 5.1-cFABP was translated and produced only pI 5.1-cFABP as shown by isoelectric focusing of the translation products. We could observe co-translational acetylation but not post-translational deamidation of the cFABP isoforms. Taken together, our results demonstrate that the isoforms of cardiac fatty-acid-binding protein found in bovine heart are coded by distinct mRNA species.

Amides↗
PubMed1993

Matrix-assisted ultraviolet laser desorption/ionization mass spectrometry applied to multiple forms of lipases.

Matrix-assisted ultraviolet laser desorption/ionization mass spectrometry was used to investigate heterogeneous patterns and molecular masses of microbial lipases from Penicillium camembertii, Geotrichum candidum, and Pseudomonas sp. Mass spectral peaks of the native, glycosylated lipases from P. camembertii and G. candidum were broader than those of the corresponding deglycosylated enzymes, indicative of heterogeneous glycosylations. The broader peaks in the mass spectra were caused by an overlapping of unresolved peaks, derived from single glycoprotein species. Molecular masses determined for the deglycosylated proteins were in excellent agreement with those deduced from amino acid composition and sequence data, whereas with conventional biochemical methods (gelfiltration, sodium dodecyl sulfate-polyacrylamide gel electrophoresis) only very rough estimations of molecular masses were possible. By mass spectrometric analysis of the four fractions of chromatographically separated P. camembertii lipase molecular masses of 29,990, 34,030, 31,990, and 32,140 Da were found before and 29,960, 29,980, 29,990 and 30,010 Da, respectively, after deglycosylation. Thus from the four native fractions of P. camembertii lipase three were glycoproteins. G. candidum lipase showed an average molecular mass of 63,500 Da for the heterogeneously deglycosylated native form and a molecular mass of 59,650 Da for the deglycosylated enzyme. For the Pseudomonas lipase, which could only be isolated with lipids firmly attached, a molecular mass of 32,890 Da was determined, in close agreement with that derived from the cDNA sequence.

Bacterial Proteins↗
PubMed1993

Effect of clofibric acid on the turnover of the fatty acid-binding protein identified in cultured endothelial cells from bovine aorta.

Several types of fatty acid-binding proteins are found in mammalian cells. Cultured endothelial cells from bovine aorta were shown to contain exclusively the cardiac-type fatty acid-binding protein (cFABP) with a mean concentration of 90 ng cFABP/mg extract protein. Only small variations were observed from passage to passage. In pulse-chase labeling experiments with L-[35S]methionine, a half-life of 4.0 d was measured for cFABP which is about two times longer than the average half-life of the extracted proteins. These data imply that in aortic endothelial cells cFABP is not subject to short-term regulation. However, addition of clofibric acid to the culture medium led to a shortening of the half-life of cFABP, which was compensated for by an increase in its biosynthesis. The turnover of the bulk of extract proteins remained unchanged when the cells were challenged with clofibric acid.

Animals↗
PubMed1993

Fatty acid-binding protein from rat heart is phosphorylated on Tyr19 in response to insulin stimulation.

The cytosolic fatty acid-binding protein from rat heart (H-FABP, M(r) 15,000) as well as FABP from mouse adipocytes (A-FABP, 62% homologous with H-FABP) contain a recognition sequence for protein tyrosine kinases, Asn-Phe-Asp-Asp-Tyr19. A-FABP has been shown by others to be partly phosphorylated on Tyr19, thus encouraging experiments designed to search for phosphotyrosine in H-FABP. For this purpose isolated cardiac myocytes were incubated with [32P]orthophosphate and analyzed by two-dimensional gel electrophoresis. A 15 kDa phosphoprotein present in the cytosolic protein fraction was specifically precipitated by a polyclonal antibody against rat heart FABP. Characterization of the phosphorylated FABP was facilitated by the development of an immunoaffinity purification procedure capable of isolating more than 200 micrograms FABP from four rat hearts in one step. Phosphoamino acid analysis and radiosequencing of the major tryptic phosphopeptide from immunopurified FABP revealed Tyr19 as the phosphorylated amino acid. Stimulation of cardiac myocytes with insulin in the presence of tyrosine phosphatase inhibitors led to a several-fold increase in the amount of phosphorylated FABP compared with a nearly undetectable level found without insulin stimulation, indicating that FABP may be a substrate for the insulin receptor tyrosine kinase. Phosphorylated FABP constitutes only a minor fraction compared to the large pool of FABP in the cardiac myocyte, thus obscuring the significance of this modification. However, as the phosphorylated Tyr19 residue is positioned within a helix-turn-helix-related domain of FABP, this modification may modulate a hitherto unknown DNA binding activity of FABP. A hypothesis is discussed in which phosphorylated FABP serves as a signalling molecule in the insulin signal transduction cascade.

Amino Acid Sequence↗
PubMed1992

Sequence-specific 1H-NMR assignment and determination of the secondary structure of bovine heart fatty-acid-binding protein.

The nearly complete sequence-specific 1H resonance assignment of the pI = 4.9 isoform of cytosolic 15-kDa fatty-acid-binding protein from bovine heart (H-FABPc) by homonuclear two-dimensional NMR spectroscopy is presented. Regular secondary structure elements were identified from NOE spectra and the sequence locations of slowly exchanging backbone amide protons. The molecular structure of the protein was found to consist mainly of ten antiparallel beta-strands and two short alpha-helices. The data presented here for the first time for a hydrophobic molecule transporter of the fatty-acid-binding protein type is the basis for a complete tertiary structure determination currently in progress.

Amino Acid Sequence↗
PubMed1992

Suppression of a ligand operated membrane current by the epileptogenic agent pentylenetetrazol in oocytes of Xenopus laevis after injection of rat brain RNA.

The effects of the epileptogenic substance pentylenetetrazol (PTZ) on ligand operated membrane channels were studied. For this purpose serotonin (5-HT) sensitive channels were expressed in RNA injected oocytes of Xenopus laevis. With simultaneous application of both substances, the response to 5-HT was reduced and eventually abolished by PTZ with increasing concentrations (5-100 mM). A reduction of the 5-HT response also appeared when PTZ was applied in various intervals (15 and 240 s) before 5-HT. It may be assumed that PTZ produces a component of its epileptogenic effect by acting on ligand operated membrane channels.

Animals↗
PubMed1991

Three-dimensional structure of fatty-acid-binding protein from bovine heart.

The complex of fatty-acid-binding protein (FABP) from bovine heart (cFABP, pI4.9) with endogenous lipid was crystallized in the presence of ammonium sulfate as precipitant. The needle-shaped crystals belong to the monoclinic space group C2, with unit-cell constants a = 5.262(6) nm, b = 7.631(8) nm, c = 3.945(5) nm and beta = 94.47(9) degrees. A native data set to 0.35 nm resolution was collected using synchrotron radiation and film methods. An initial model for the three-dimensional structure of the protein was constructed based on the crystal structure of the related bovine P2 myelin protein [Jones, T.A., Bergfors, T., Sedzik, J. & Unge, T. (1988) EMBO J. 7, 1597-1604] to which the amino acid sequence of bovine cFABP was adapted. Energy minimizations were carried out under different conditions using both an all-atom and a united-atom force field. The optimized models were used to determine the crystal structure of cFABP by molecular-replacement techniques. The structure was refined by simulated annealing to R = 0.267. As the bound lipid is heterogeneous, it could not be located in the electron-density map and/or the attained resolution was not sufficient. Bovine cFABP is composed of ten antiparallel beta strands forming a beta barrel, and by two alpha helices. The structural features are similar to those of other members of the superfamily of hydrophobic molecule transporters.

Amino Acid Sequence↗
PubMed1990

Cardiac fatty acid-binding proteins. Isolation and characterization of the mitochondrial fatty acid-binding protein and its structural relationship with the cytosolic isoforms.

In the course of our studies on the structural diversity of the isoforms of cardiac fatty acid-binding proteins (cFABPs), a cardiac-type FABP from the matrix of bovine heart mitochondria was purified to homogeneity and obtained as a single 15-kDa protein with an isoelectric point of 4.9. The primary structures of this protein and of the two isoforms isolated from the cytosol (pI4.9-cFABP and pI 5.1-cFABP) were investigated by means of plasma desorption mass spectrometry and sequencing of peptides. All three proteins are amino-terminally blocked with an acetyl group and shown to be colinear with the sequence deduced from a cDNA clone for bovine heart fatty acid-binding protein (Billich, S., Wissel, T., Kratzin, H., Hahn, U., Hagenhoff, B., Lezius, A. G., and Spener, F. (1988) Eur. J. Biochem. 175, 549-556) except for the residue at position 98. This residue is demonstrated to be the molecular origin of bovine cFABP isoforms since pI 5.1-cFABP contains Asn98 in accordance with the sequence derived from the cDNA, whereas in pI 4.9-cFABP, this position is occupied by Asp98. Moreover, mitochondrial FABP is identical to pI 4.9-cFABP. Molecular masses of pI 4.9-cFABP (14,679 +/- 10 Da) and pI 5.1-cFABP (14,678 +/- 20 Da) determined by plasma desorption mass spectrometry coincide with that calculated from the cDNA (14,673 Da). Hence, residues linked to these proteins by posttranslational modification are not present, and the Asn-Asp exchange is the sole origin of heterogeneity of mitochondrial and cytosolic fatty acid-binding proteins from bovine heart.

Amino Acid Sequence↗
PubMed1990

Two-dimensional electrophoresis of the fatty acid binding protein from human heart: evidence for a thiol group which can form an intermolecular disulfide bond.

A 100,000 g supernatant from human heart muscle, containing cytosolic proteins with some contaminating plasma proteins, was analyzed for fatty acid binding protein (FABP) by two-dimensional electrophoresis (2-DE) using isoelectric focusing under nondenaturing conditions in the first dimension. FABP purified from human heart muscle was found to comigrate with a major spot in 2-DE gels of the supernatant. This spot was comparable with those of the myoglobins in staining intensity. When purified FABP was charged with [3H]palmitate and subjected to nondenaturing 2-DE, radioactivity always comigrated with this protein. Under denaturing and reducing conditions in the second dimension, FABP was found to have a pI of 5.3 and an apparent molecular weight of 15,000. Isoforms of FABP, reported here for the first time to occur in human heart muscle, were observed as minor spots focusing at pH 5.1 and 5.7. When electrophoresis in the second dimension was carried out under denaturing but nonreducing conditions, an additional protein appeared at pH 5.3 with an apparent molecular weight of about 30,000. This protein was identified as a dimer of FABP and evidence for the involvement of an intermolecular disulfide bond in this dimerization is presented.

Carrier Proteins↗