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D M Haverstick

Publications and source records attributed to D M Haverstick.

36 records · Page 2Linked to original sources
PubMed1989

Influence of proteins on the reorganization of phospholipid bilayers into large domains.

Using large (5-10 microns) vesicles formed in the presence of phospholipids fluorescently labeled on the acyl chain and visualized using a fluorescence microscope, charge-coupled-device camera, and digital image processor, we examined the effects of membrane proteins on phospholipid domain formation. In vesicles composed of phosphatidic acid and phosphatidylcholine, incubation with cytochrome c induced the reorganization of phospholipids into large phosphatidic acid-enriched domains with the exclusion of phosphatidylcholine. Cytochrome c binding was demonstrated to be highest in the phosphatidic acid-enriched domain of the vesicle using the absorbance of the heme moiety for visualization. Both binding of cytochrome c and phospholipid reorganization were blocked by pretreatment of the vesicles with 0.1 M NaCl. The pore forming peptide gramicidin was examined for the effects of an integral protein on domain formation. Initially, gramicidin distributed randomly within the vesicle and showed no phospholipid specificity. Phosphatidic acid domain formation in the presence of 2.0 mM CaCl2 or 100 microM cytochrome c was not affected by the presence of 5 mol % gramicidin within the vesicles. In both cases, gramicidin was preferentially excluded from the phosphatidic acid-enriched domain and became associated with phosphatidylcholine-enriched areas of the vesicle. Thus, cytochrome c caused a major reorganization of both the phospholipids and the proteins in the bilayer.

Cytochrome c Group↗
PubMed1989

Striatal tachykinin gene expression regulated by interaction of D-1 and D-2 dopamine receptors.

The involvement of D-1 and D-2 dopamine (DA) receptors in mediating the DA regulation of preprotachykinin (PPT) gene expression was investigated in rat striatal tissue. Initial experiments determined that acute treatment with the indirect DA agonist methamphetamine induces increases in total PPT messenger RNA, with a maximal effect seen within 3 hr. RNA protection studies established that acute methamphetamine treatment did not affect the relative ratios of the various PPT gene transcripts derived by alternate splicing. The methamphetamine-induced increase in total PPT messenger RNA could be blocked by either a D-1 or a D-2 selective DA antagonist (SCH 23390 and sulpiride, respectively). The D-2 agonist quinpirole, but not the D-1 agonist SKF 38393, mimicked the methamphetamine-induced increase. This D-2 agonist-induced increase was dependent upon D-1 receptor tone, as either co-administration of SCH 23390 or pretreatment with the DA synthesis inhibitor alpha-methyltyrosine blocked the quinpirole-induced increase. These studies provide biochemical evidence for an enabling role of D-1 DA receptors in striatal D-2 DA receptor function.

Animals↗
PubMed1988

Visualization of domain formation in the inner and outer leaflets of a phospholipid bilayer.

Large vesicles (5-10-micron in diameter) were formed in the presence of phospholipids fluorescently labeled on the acyl chain and visualized using a fluorescence microscope, charge-coupled-device camera and digital image processor. When such vesicles contained a fluorescent phosphatidic acid (PA) and were exposed to 2 mM CaCl2 or 0.5 mM PrCl3, it was possible to visualize PA-enriched domains within the vesicles. Calcium-induced domain formation was reversible in the presence of 4 mM EGTA. Vesicles were formed containing fluorescent PA on either the inner or outer leaflet of the bilayer and the patching and dissolution of patching were studied under conditions where calcium was present on the outside of the vesicle and where calcium was distributed across the bilayer. In addition, vesicles were formed with two different fluorescent PA's, one on the inner leaflet and a different one on the outer leaflet of the bilayer. The results of the experiments show that in vesicles formed primarily with naturally occurring phospholipids such as egg phosphatidylcholine or brain phosphatidylethanolamine, there was no coordinate action of the two leaflets of the bilayer. An exception to this was found, however, if the vesicles were formed in the presence of primarily dioleoyl phospholipids (greater than 95 mol %). In these vesicles there was a coordinate or coupled response to calcium by the two leaflets of the bilayer. In most cases, however, the two leaflets of the bilayer showed independent or uncoupled domain formation.

Calcium↗
PubMed1987

Visualization of Ca2+-induced phospholipid domains.

Large vesicles (5-15 microns) were formed by hydrating a dried lipid film containing phospholipids labeled with a fluorophore in one fatty acid chain. By using a fluorescence microscope attached to a low-light-intensity charge-coupled-device camera and digital-image processor, the vesicles were easily viewed and initially showed uniform fluorescence intensity across the surface. The fluorescence pattern of vesicles made with a fluorophore attached to phosphatidylcholine or phosphatidylethanolamine was unaffected by the presence of divalent cations such as Ca2+, Mg2+, Mn2+, Zn2+, or Cd2+. The fluorescence pattern of vesicles containing a fluorophore attached to the acidic phospholipids phosphatidylserine or phosphatidic acid showed distinct differences when treated with Ca2+ or Cd2+, although they were unaffected by Mg2+, Mn2+, or Zn2+. Treatment with 2.0 mM Ca2+ or Cd2+ resulted in the movement of the fluorophore to a single large patch on the surface of the vesicle. When vesicles were formed in the presence of 33 mol % cholesterol, patching was seen at a slightly lower Ca2+ concentration (1.0 mM). The possibility of interactions between Ca2+ and acidic phospholipids in plasma membranes was investigated by labeling erythrocytes and erythrocyte ghosts with fluorescent phosphatidic acid. When Ca2+ was added, multiple (five or six) small patches were seen per individual cell. The same pattern was observed when vesicles formed from whole lipid extracts of erythrocytes were labeled with fluorescent phosphatidic acid and then treated with Ca2+. This shows that the size and distribution of the Ca2+-induced domains depend on phospholipid composition.

Animals↗
PubMed1985

The platelet glycoprotein thrombospondin binds specifically to sulfated glycolipids.

The human platelet glycoprotein thrombospondin (TSP) binds specifically and with high affinity to sulfatides (galactosylceramide-I3-sulfate). Binding of 125I-TSP to lipids from sheep and human erythrocytes and human platelets resolved on thin layer chromatograms indicates that sulfatides are the only lipids in the membrane which bind TSP. Binding to less than 2 ng of sulfatide could be detected. TSP failed to bind to other purified lipids including cholesterol 3-sulfate, phospholipids, neutral glycolipids, and gangliosides. Binding of 125I-TSP was inhibited by unlabeled TSP, by low pH, and by reduction of intersubunit disulfide bonds with dithiothreitol. A monoclonal antibody against TSP (A2.5), which inhibits hemagglutination and agglutination of fixed activated platelets by TSP, strongly inhibited TSP binding to sulfatides. A second monoclonal antibody (C6.7), which inhibits hemagglutination and aggregation of thrombin-activated live platelets, weakly inhibited sulfatide binding. Binding was inhibited by high ionic strength and by some monosaccharide sulfates including methyl-alpha-D-GlcNAc-3-sulfate. Neutral sugars did not inhibit. Fucoidan, a sulfated fucan, strongly inhibited binding with 50% inhibition at 0.3 micrograms/ml fucoidan. Other sulfated polysaccharides including heparin and dextran sulfates were good inhibitors, whereas hyaluronic acid and keratan sulfate were very weak.

Animals↗
PubMed1985

Effects of anti-thrombospondin monoclonal antibodies on the agglutination of erythrocytes and fixed, activated platelets by purified thrombospondin.

A monoclonal antibody (Mab) has been raised against native thrombospondin (TSP), the endogenous lectin of human platelets, that inhibits the hemagglutination of trypsinized, glutaraldehyde-fixed human erythrocytes by purified TSP. This Mab, designated A2.5, also inhibits the agglutination of fixed, activated platelets by TSP. Mab A2.5 immunoprecipitates a 25-kilodalton (kDa) peptide from chymotryptic digests of TSP that is not disulfide bonded to any other region of the TSP molecule. This fragment represents the previously characterized heparin binding domain of TSP [Dixit, V.M., Grant, G.A., Santoro, S.A., & Frazier, W.A. (1984) J. Biol. Chem. 259, 10100-10105]. In agreement with this assignment, heparin inhibits the binding of Mab A2.5 to TSP. Another Mab, designated C6.7, also blocks TSP-mediated hemagglutination, yet has no effect on the agglutination of fixed, activated platelets by TSP. This Mab has been shown to inhibit the thrombin-stimulated aggregation of live platelets and to immunoprecipitate an 18-kDa fragment from chymotryptic digests, which is distinct from the heparin binding domain [Dixit, V.M., Haverstick, D.M., O'Rourke, K.M., Hennessy, S.W., Grant, G.A., Santoro, S.A., & Frazier, W.A. (1985) Proc. Natl. Acad. Sci. U.S.A. 82, 3472-3476].

Antibodies, Monoclonal↗
PubMed1985

Characterization of the platelet agglutinating activity of thrombospondin.

Thrombospondin (TSP) is a glycoprotein secreted from the alpha-granules of platelets upon activation. In the presence of divalent cations, the secreted protein binds to the surface of the activated platelets and is responsible for the endogenous lectin-like activity associated with activated platelets. Platelets fixed with formaldehyde following activation by thrombin are agglutinated by exogenously added TSP. Fixed, nonactivated platelets are not agglutinated. The platelet agglutinating activity of TSP is optimally expressed in the presence of 2 mM each of Mg2+ and Ca2+. Reduction of the disulfide bonds within the TSP molecule inhibits its platelet agglutinating activity. TSP bound to the surface of fixed, activated platelets can be eluted by the addition of disodium ethylenediaminetetraacetate. This approach was exploited to identify the region of the TSP molecule containing the platelet binding site. The binding site resides within a thermolytic fragment of TSP with Mr 140 000 but is not present in the Mr 120 000 fragment derived from the polypeptide of Mr 140 000. Since both the Mr 140 000 and 120 000 fragments contain fibrinogen binding sites, this finding suggests that the binding of TSP to the platelet surface requires interaction with other platelet surface components in addition to fibrinogen. The observation that fibrinogen only partially inhibits the TSP-mediated agglutination of fixed, activated platelets is consistent with this interpretation.

Blood Platelets↗
PubMed1985

Some properties of a liver protein that activates glycogen synthase b.

A soluble protein has been identified in rat liver that increases the activity of glycogen synthase without causing synthase b to a conversion. The effect of the activator is to increase synthase b activity in the presence of saturating amounts of UDP-Glc and Glc-6-P. The activator is heat sensitive and does not have protease activity. The effect of the activator is linearly proportional to the amount assayed to a saturable level and its effect is not mimicked by other proteins associated with the control of glycogen metabolism (e.g., phosphorylase).

Animals↗
PubMed1985

A monoclonal antibody against human thrombospondin inhibits platelet aggregation.

A monoclonal antibody (C6.7) has been generated against the calcium-replete form of human platelet thrombospondin (TSP). C6.7 is specific for TSP as determined by both competitive radioimmunoassay and immunoprecipitation. This antibody inhibits both thrombin- and A23187-induced aggregation of gel-filtered platelets in a concentration-dependent manner without affecting the secretion of serotonin. The epitope on TSP recognized by C6.7 has been localized to an 18-kDa fragment that is present in mild chymotryptic digests of TSP. This fragment is disulfide-linked to a 120- to 140-kDa fragment in unreduced digests, and both reduction and denaturation are required to separate the 18-kDa peptide from the larger fragments. A 25-kDa heparin binding domain is also present in the chymotryptic digest. However, the 18-kDa peptide is distinct from the heparin binding domain. The amino acid sequence at the NH2 terminus of the 18-kDa fragment is Asp-Thr-Asn-Pro-Thr-Arg-Ala-Gln-Gly-Tyr-.

Amino Acid Sequence↗
PubMed1985

Inhibition of platelet aggregation by a monoclonal antibody against human fibronectin.

A monoclonal antibody (A3.3) has been generated against human platelet fibronectin (FN). A3.3 reacts with human plasma FN but with no other plasma proteins. A3.3 was found to inhibit thrombin- or ionophore A23187-stimulated aggregation of gel-filtered platelets in a concentration-dependent manner in both an aggregometer assay and a sensitive well plate aggregation assay. The antibody does not block secretion of serotonin. Four other anti-FN monoclonal antibodies that recognize different epitopes on FN than A3.3 does have no effect on platelet aggregation. A3.3 does not block the adhesion of CHO cells to FN-coated surfaces, indicating that it does not bind to the identified cell-binding domain of FN. A3.3 reacts with a 160/140-kDa doublet, known to contain the cell-binding domain, that is produced by digestion of FN with elastase or thermolysin. However, the antibody does not react with lower molecular weight species that also contain the cell-binding domain or with any of the other identified domains of FN. The A3.3 epitope is extremely protease sensitive and the smallest fragment found in any digest that retains reactivity with A3.3 is a 70-kDa peptide produced in low yield by mild thermolytic cleavage of FN. These data suggest that A3.3 defines a functional site present on both the platelet and plasma FN molecule that has a direct role in platelet aggregation.

Animals↗
PubMed1985

Inhibition of platelet adhesion to fibronectin, fibrinogen, and von Willebrand factor substrates by a synthetic tetrapeptide derived from the cell-binding domain of fibronectin.

The role in platelet function of the cell-binding region of fibronectin was explored by the use of synthetic peptides. The prototypical peptide gly-arg-gly-asp-ser was capable of inhibiting thrombin-induced platelet aggregation without altering the degree of platelet activation as judged by the secretion of 14C-serotonin. The peptide also effectively inhibited, in a concentration-dependent manner, the binding of radiolabeled fibronectin to platelets and the adhesion of platelets to fibronectin substrates. The smallest peptide from the cell-binding region of fibronectin which retained full activity was arg-gly-asp-ser. Transposition of amino acids or conservative substitutions of amino acids within this short sequence resulted in inactive peptides. Peptides containing the arg-gly-asp-ser sequence were also capable of inhibiting the adhesion of platelets to fibrinogen and von Willebrand factor substrates. Examination of the entire panel of synthetic peptides for ability to inhibit adhesion to fibrinogen or von Willebrand factor substrates revealed the same structure-function relationships that had been determined in the studies with fibronectin.

Amino Acid Sequence↗
PubMed1984

Localization of the hemagglutinating activity of platelet thrombospondin to a 140 000-dalton thermolytic fragment.

The platelet protein thrombospondin (TSP) which is secreted from alpha-granules upon platelet activation agglutinates trypsinized, glutaraldehyde-fixed human erythrocytes. Optimal conditions for the hemagglutinating activity require that both Ca2+ and Mg2+ be present in final concentrations of 2 mM. In the presence of dithiothreitol (i.e., reduction of disulfide bonds), the lectin-like activity decreases in a manner proportional to the extent of reduction of the molecule from its native trimeric configuration into its Mr 180 000 subunits. Proteolysis of purified TSP with thermolysin, which produces discrete domains with the capacity to bind fibrinogen and heparin, also diminishes, but does not abolish, the hemagglutinating activity. Fibrinogen was without effect on hemagglutinating activity while heparin was found to be a potent inhibitor. Other proteoglycans such as hyaluronic acid, chondroitin sulfate, keratan sulfate, dermatan sulfate, and heparan sulfate had no effect. That portion of the TSP molecule apparently responsible for the hemagglutinating activity was identified by incubating a thermolytic digest of TSP with red blood cells and then determining which fragment was bound to the cell surface. The binding site resides within a peptide fragment of 140 000 daltons but is absent from an Mr 120 000 fragment derived from the Mr 140 000 fragment. Under the conditions for optimal expression of hemagglutinating activity (i.e., 2 mM MgCl2 and 2 mM CaCl2), this Mr 140 000 fragment was also shown to have heparin binding activity.

Blood Platelets↗
PubMed1980

Comparative catalytic properties of liver glycogen synthases from adult and newborn rats.

Liver glycogen synthases have been isolated from adult and newborn rats. Comparative catalytic properties show that adult synthase, which undergoes covalent modification resulting in an altered enzyme activity related to the need for glycogen synthesis, has properties consistent with the hypothesis that the alpha (dephosphorylated) enzyme is that which is physiologically active in vivo when liver glycogen is synthesized. Synthase from the newborn, which does not show an endogenous b into a transformation, has catalytic characteristics similar to the adult a-type synthase. However, the newborn synthase is absolutely dependent on Glc-6-P for activity, as is the adult-type synthase b. A comparison of the effects of Glc-6-P and UDP-Glc on Pi and ATP inhibition of the adult and newborn synthases suggest the "apparent" b-type synthase from the newborn is more subject to metabolite regulation of activity than the adult-type b enzyme.

Aging↗
PubMed1979

Insulin sensitivity of liver glycogen synthase b into a conversion.

Liver glycogen synthase b phosphatase, chromatographically separable from phosphorylase a phosphatase, is decreased in 48-hour alloxan diabetic rats. The phosphatase activities are measured in an in vitro system using exogenous isolated phospho-enzyme as substrates with added phosphatases. Synthase and phosphorylase phosphatases were shown to have differential catalytic properties by their reactivity in the presence of Pi, the heat-stable inhibitor of phosphorylase phosphatase and after incubation with added cAMP-dependent protein kinase.

Animals↗
PubMedDate not supplied

Modifications to the in situ TUNEL method for detection of apoptosis in paraffin-embedded tissue sections.

The in situ detection of cells undergoing apoptosis is increasingly important in the analysis of injury and degeneration in the central nervous system. Limited information is presently available on the quantification of apoptosis in paraffin-embedded brain tissue sections, a technique which would be most useful in the evaluation of archival tissue for diagnostic and experimental purposes. In this report, optimized conditions for tissue digestion and permeabilization using Proteinase K and Triton X and a quantification method for apoptosis detection are described using brain sections from aluminum maltolate-treated aged and young rabbits as compared to untreated matched controls. This method provides optimal staining of apoptotic cells without the problem of tissue destruction, and should prove useful in evaluating the process of apoptosis in neurodegenerative disorders.

Aging↗