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D W Jacobsen

Publications and source records attributed to D W Jacobsen.

At least 73 records · Page 4Linked to original sources
PubMed1988

Kinetics and activation parameters of the reaction of cyanide with free aquocobalamin and aquocobalamin bound to a haptocorrin from chicken serum.

The kinetics of the reaction of cyanide with free aquocobalamin (H2OCbl) and with aquocobalamin bound to a vitamin B12-binding protein (haptocorrin) from chicken serum (HC-H2OCbl) have been investigated as a function of temperature and pH. The mechanism of replacement of H2O from protein-bound and free H2OCbl is apparently the same and involves attack of both CN- (k1) and HCN (k2). The reactions with HC-H2OCbl are somewhat slower than those with free H2OCbl, k1 being 22-fold smaller and k2 7-fold smaller at 25 degrees C. The relatively small effect of the protein on the rate constants supports the view that the metal in HC-H2OCbl is readily accessible to solvent. Activation parameters suggest that the transition states for ligand substitution are stabilized by nucleophilic participation (at least by CN-) and that ligand substitution on the protein-bound cobalamin proceeds through more ordered, concerted transition states. The latter effect suggests that the Co-O bond of H2OCbl is strengthened upon binding to the haptocorrin.

Animals↗
PubMed1988

Heteronuclear NMR studies of cobalamins. 31P NMR observations of cobalamins bound to a haptocorrin from chicken serum.

A vitamin B12-binding protein (haptocorrin) from chicken serum has been purified to homogeneity by photodissociative affinity chromatography and characterized by gel electrophoresis and UV-visible spectrophotometry of its aquocobalamin, hydroxocobalamin, and cyanocobalamin complexes. The haptocorrin is a glycoprotein with a molecular mass of about 70 kDa and a protein moiety of about 40 kDa. 31P NMR resonances of the haptocorrin-cobalamin complexes are relatively broad singlets (with or without proton decoupling) shifted downfield by 0.7-1.0 ppm from the position of the free cobalamin resonances. From the line width data, the relaxation of the phosphorus nucleus is found to be dominated by chemical shift anisotropy with a very minor (13%) component from dipolar interaction with the two nearest neighbor protons. The rotational correlation time of the haptocorrin at 25 degrees C is estimated to be 85 ns and the activation energy for rotational correlation 3.9 +/- 0.3 kcal mol-1. The downfield shift of the 31P resonances of cobalamins upon binding to the haptocorrin cannot be due to hydrogen bonding phosphodiester moiety or displacement of the axial base by a group on the protein. Calculations also show that the downfield shift is very unlikely to be due to dipolar deshielding of the phosphorus nucleus by the ring current of an aromatic residue of the protein. It is concluded that the downfield shift of the 31P resonance must be due to sterically induced changes in phosphodiester conformation which may, or may not, involve steric compression of the axial Co-N bond.

Algorithms↗
PubMed1987

Receptors for transferrin and transcobalamin II display segregated distribution on microvilli of leukemia L1210 cells.

Simultaneous addition of uniform latex particles derivatized with transferrin (0.532 micron) and transcobalamin II (0.345 micron) to leukemia L1210 cells resulted in segregated binding to individual microvilli as demonstrated by scanning electron microscopy. This segregated distribution suggests that individual microvilli are endowed either transferrin or transcobalamin II receptors but not both. Intracellular sorting and segregation of newly synthesized or recycling receptors probably occur prior to expression on the plasmalemma microvilli.

Animals↗
PubMed1987

Sulfite hypersensitivity. A critical review.

Sulfiting agents (sulfur dioxide and the sodium and potassium salts of bisulfite, sulfite, and metabisulfite) are widely used as preservatives in foods, beverages, and pharmaceuticals. Within the past 5 years, there have been numerous reports of adverse reactions to sulfiting agents. This review presents a comprehensive compilation and discussion of reports describing reactions to ingested, inhaled, and parenterally administered sulfite. Sulfite hypersensitivity is usually, but not exclusively, found within the chronic asthmatic population. Although there is some disagreement on its prevalence, a number of studies have indicated that 5 to 10% of all chronic asthmatics are sulfite hypersensitive. This review also describes respiratory sulfur dioxide sensitivity which essentially all asthmatics experience. Possible mechanisms of sulfite hypersensitivity and sulfur dioxide sensitivity are discussed in detail. Sulfite metabolism and the role of sulfite oxidase in the detoxification of exogenous sulfite are reviewed in relationship to the etiology of sulfite hypersensitivity.

Administration, Oral↗
PubMed1987

Lactoferrin binding by leukemia cell lines.

Monocytes and macrophages have receptors for the iron-binding protein lactoferrin. Lactoferrin acts as a potent inhibitor of granulocyte-macrophage colony stimulating factor production when it binds to these cells. Using a rosette assay and immunofluorescence, we have shown that cultured leukemia cells, including the human erythroid leukemia cell line K562, also have lactoferrin binding sites. The number of binding sites on K562 cells was estimated using soluble 59Fe-lactoferrin. Inhibition studies demonstrate that lactoferrin binding sites are distinct and unrelated to receptors for transferrin or the Fc portion of IgG, which are present on K562 cells. However, electrostatic forces may be important for lactoferrin binding, since other polycationic proteins (eg, protamine) inhibit lactoferrin binding. Prior treatment of K562 cells with trypsin nearly abolishes lactoferrin binding. However, these cells recover their ability to bind lactoferrin when trypsin is removed. Unlike transferrin receptors, the expression of lactoferrin binding sites is not regulated by cellular iron status. Cytosine arabinoside arrests the proliferation of K562 cells and simultaneously leads to a reduction in lactoferrin surface binding, suggesting that lactoferrin binding may be dependent on cell proliferation.

Cell Division↗
PubMed1986

Visualization of the receptor for transferrin on K562 cells by a rosette-forming assay.

A method is described to visualize the receptor for transferrin by a rosette-forming assay. K562 cells, a human pre-erythroid leukemia cell line, were used as a source of receptor-positive cells. Bovine erythrocytes coated with human transferrin by the CrCl3 method were used as indicator cells. Rosette formation occurred at 37 degrees C but not at 4 degrees C, and was inhibited by soluble transferrin in a dose-dependent manner. Human lactoferrin, which is known to have considerable amino acid sequence homology with transferrin, did not inhibit rosette formation with transferrin-coated bovine erythrocytes. A variety of blocking and non-blocking monoclonal antibodies against the human transferrin receptor (42/6, B3/25 and OKT9) inhibited rosette formation. Rosettes are able to withstand low-speed centrifugation (130 X g, 2 min) making this method potentially useful for cytochemical identification of receptor-positive or receptor-negative cells. Also, it was possible to enrich receptor-positive cells by separation of rosette-forming from non-rosette-forming cells using a density gradient centrifugation technique.

Animals↗
PubMed1985

Receptor distribution and the endothelial uptake of transcobalamin II in liver cell suspensions.

To determine the nature of binding of transcobalamin II (TC-II) to liver cells, we covalently coupled purified holo-TC-II to submicron latex minibeads using glutaraldehyde. Incubation of the probe with liver cell suspensions at 4 degrees C led to its binding by endothelial cells but not by hepatocytes or Kupffer cells, as visualized by scanning electron microscopy. At 37 degrees C, the probe was internalized by the endothelium through a system of coated pits and vesicles as shown by transmission electron microscopy. Inhibition studies by pre-incubation with excess native TC-II demonstrated the specificity of binding. Fractionation of these cell suspensions on metrizamide gradients yielded large cell (hepatocyte-rich) and small cell (endothelium-rich) fractions. The binding of the minibead probe occurred again exclusively on endothelial cells in the small cell fraction. 125I-labeled holo-TC-II also bound to the small cell but not to the large cell fraction. Binding was saturable (Ka, 0.225 X 10(9) mol/L-1) and receptor number was calculated to be 1.33 X 10(3) per cell. Time-dependent incubation of 125I-labeled TC-II with the endothelium-rich fraction led to its uptake, reaching a steady-state plateau at 4 degrees C. At 37 degrees C, however, the initial uptake was followed by gradual release of the label into the medium. We conclude that in the liver, holo-TC-II binds initially to endothelium, where it is internalized and is subsequently released probably to the interstitial space. Thus, the endothelium may play a fundamental role in the regulation of the uptake of TC-II by the liver.

Animals↗
PubMed1982

Absorption of biliary cobalamin in baboons following total gastrectomy.

Absorption of radiolabeled cobalamin in baboons was assessed by whole body counting. Retention of biliary cobalamin and an aqueous solution of cyanocobalamin was measured in normal baboons and in baboons after total gastrectomy by using 57Co-labeled biliary cobalamin and 58C0-cyanocobalamin, with and without baboon gastric juice containing intrinsic factor. Radiolabeled biliary cobalamin was obtained by intravenous injection of 57Co-cyanocobalamin in baboons and collection of bile through a cannula placed in the common bile duct. Cobalamin absorption was not completely abolished by gastrectomy and biliary cobalamin was better retained than cyanocobalamin; intrinsic factor enhanced absorption of both forms. After gastrectomy there was steady depletion of liver and serum cobalamin levels, which ceased after a new equilibrium was reached between a progressively diminishing cobalamin loss and the impaired but significant residual level of absorption. These studies in the nonhuman primate provide further information concerning the enterohepatic circulation of cobalamin and suggest that the form of cobalamin in bile may be more readily absorbed than is cyanocobalamin or that bile itself may have an enhancing effect on cobalamin absorption. The data also suggest that physiologically significant amounts of cobalamin may be absorbed in the absence of a gastric source of intrinsic factor.

Absorption↗
PubMed1981

Enterohepatic circulation of cobalamin in the nonhuman primate.

Biliary excretion of cobalamin was studied in baboons after intravenous injection of 57Co-radiolabeled cyanocobalamin. Radioactivity appeared in bile after 20 min, and up to 4.4% of the dose was recovered in 6 h. It was estimated that 4 microgram cobalamin traverses the baboon biliary tract each day. These studies in the nonhuman primate confirm that there is considerable biliary excretion of cobalamin and that enterohepatic circulation of the vitamin is important for maintenance of normal cobalamin balance.

Animals↗
PubMed1980

Receptor binding and internalization of immobilized transcobalamin II by mouse leukaemia cells.

Membrane transport of vitamin B12 (cyanocobalamin; Cbl) into mammalian cells is mediated by the serum protein transcobalamin II (TCII). In mouse leukaemia L1210 cells, TCII-Cbl binds to membrane receptors in a rapid, temperature-independent step and is internalized by a slow, temperature-dependent process. To delineate the location of receptors on these cells, we have constructed a visual probe by covalently coupling purified TCII-Cbl to submicrometre latex particles (minibeads). We report here that when L1210 cells are incubated with minibeads containing TCII-Cbl at 4 degrees C and examined by scanning electron microscopy (SEM), the particles are found attached predominantly to microvilli. Incubation of the cells at 37 degrees C results in the internalization of the minibeads. As visualized by transmission electron microscopy (TEM), this endocytotic process seems to occur in clathrin-coated pits and vesicles at the cell surface.

Animals↗
PubMed1980

Adherence of L1210 murine leukemia cells to sephacryl-aminopropylcobalamin beads treated with transcobalamin-II.

Sephacryl beads containing an immobilized aminopropylcobalamin-transcobalamin-II complex serve as foci for the adherence of L1210 murine leukemia cells. Bead-cell interaction does not occur when (A) nonderivatized beads are used; (B) transcobalamin-II is omitted or presaturated with cyanocobalamin in the preparation of the bead complex; (C) intrinsic factor replaces transcobalamin-II; and (D) the complex is removed from beads by photolysis. These observations suggest that adherence results from the ability of transcobalamin-II to form a bridge between immobilized cobalamin on the bead and receptors in the plasma membrane of the cell.

Acrylic Resins↗
PubMed1979

Cryptofluorescent analogs of cobalamin coenzymes: synthesis and characterization.

Upper-axial (beta-position) ligand analogs of the B12 coenzymes 5'-deoxy-5'-adenosylcob(III)alamin and methylcob(III)alamin have been synthesized by reaction of the 5'-chloro-5'-deoxy derivatives of fluorescent nucleosides (1,N6-ethenoadenosine, formycin, 2-amino-nebularine, and 2,6-diaminonebularine) and a fluorescent alkyl halide (dansylamidopropyl chloride) with cob(I)alamin. These analogs were nonfluorescent, but fluorescent products could be generated by photolysis or cyanolysis of the carbon-cobalt bonds. Under anaerobic and aerobic conditions, the major fluorescent photolysis products of 1,N6-ethenoadenosylcob(III)alamin were 1,N6-etheno-5',8-cyclic-5'-deoxyadenosine, and the 5'-aldehyde of 1,N6-ethenoadenosine, respectively. The cryptofluorescent property of these analogs was utilized to follow the kinetics of aerobic photolysis. First-order rate constants determined by this method were comparable to those obtained spectrophotometrically [via appearance of of aquacob(III)alamin]. Pseudo-first-order rate constants determined fluorometrically for the cyanolysis (at 25 degrees C) of 1,N6-ethenoadenosylcob(III)alamin, 2,6-diaminonebularinylcob(III)alamin, 2-aminonebularinylcob(III)alamin and formycinylcob(III)alamin were 5.8 X 10(-2), 2 X 10(-2), 1.8 X 10(-2), and 3 X 10(-5) min-1, respectively; values in good agreement were obtained spectrophotometrically (via appearance of dicyanocobalamin). Dansylamidopropylcob(III)alamin was stable in the presence of cyanide. The nucleoside alpha-ribazole is fluorescent in the free state but nonfluorescent when present as the lower axial (alpha-position) ligand in cobalamin coenzymes. Thus fluorescence of ligands in both the alpha- and beta-positions of cobalamins is quenched, probably as a result of intramolecular energy transfer between the ligands and the nonfluorescent corrinoid.

Aerobiosis↗