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D H Atha

Publications and source records attributed to D H Atha.

31 records · Page 2Linked to original sources
PubMed1985

Contribution of monosaccharide residues in heparin binding to antithrombin III.

The importance of 3-O- and 6-O-sulfated glucosamine residues within the heparin octasaccharide iduronic acid(1)----N-acetylglucosamine 6-O-sulfate(2)----glucuronic acid(3)----N-sulfated glucosamine 3,6-di-O-sulfate(4)----iduronic acid 2-O-sulfate(5)----N-sulfated glucosamine 6-O-sulfate(6)----iduronic acid 2-O-sulfate(7)----anhydromannitol 6-O-sulfate(8) was determined by comparing with synthetic tetra- and penta-saccharides its ability to bind human antithrombin. The octasaccharide had an affinity for antithrombin of 1 X 10(-8) M (10.2 kcal/mol) measured by intrinsic fluorescence enhancement at 6 degrees C. The synthetic pentasaccharide, consisting of residues 2-6, had an affinity of 3 X 10(-8) M (9.6 kcal/mol). The same pentasaccharide, except lacking the 3-O-sulfate on residue 4, had an affinity of 5 X 10(-4) M (4.5 kcal/mol) measured by equilibrium dialysis. The tetrasaccharide, consisting of residues 2-5, bound antithrombin with an affinity of 5 X 10(-6) M (6.8 kcal/mol). The tetrasaccharide, consisting of residues 3-6, had an affinity of 5 X 10(-5) M (5.5 kcal/mol). Since the loss of either the 6-O-sulfated residue 2 or the 3-O-sulfate of residue 4 results in a 4-5 kcal/mol or a 40-50% loss in binding energy of the pentasaccharide, these two residues must be the major contributors to the binding and must be linked to the biologic activity of the octasaccharide.

Animals↗
PubMed1984

Sequence variation in heparin octasaccharides with high affinity for antithrombin III.

We have isolated from nitrous acid cleavage products of heparin two major octasaccharide fragments which bind with high affinity to human antithrombin. Octasaccharide S, with the predominant structure iduronic acid----N-acetylglucosamine 6-O-sulfate----glucuronic acid-----N-sulfated glucosamine 3,6-di-O-sulfate----iduronic acid 2-O-sulfate----N-sulfated glucosamine 6-O-sulfate----iduronic acid 2-O-sulfate----anhydromannitol 6-O-sulfate, is sensitive to cleavage by Flavobacterium heparinase as well as platelet heparitinase and binds to antithrombin with a dissociation constant of (5-15) X 10(-8) M. Octasaccharide R, with the predominant structure iduronic acid 2-O-sulfate----N-sulfated glucosamine 6-O-sulfate----iduronic acid----N-acetylglucosamine 6-O-sulfate----glucuronic acid----N-sulfated glucosamine 3,6-di-O-sulfate----iduronic acid 2-O-sulfate----anhydromannitol 6-O-sulfate, is resistant to degradation by both enzymes and binds antithrombin with a dissociation constant of (4-18) X 10(-7) M. The occurrence of a 15-17% replacement of N-sulfated glucosamine 3,6-di-O-sulfate with N-sulfated glucosamine 3-O-sulfate and a 10-12% replacement of iduronic acid with glucuronic acid in both octasaccharides indicates that these substitutions have little or no effect on the binding of the oligosaccharides to the protease inhibitor. When bound to antithrombin, both octasaccharides produce a 40% enhancement in the intrinsic fluorescence of the protease inhibitor and a rate of human factor Xa inhibition of 5 X 10(5) M-1 s-1 as monitored by stopped-flow fluorometry. This suggests that the conformation of antithrombin in the region of the factor Xa binding site is similar when the protease inhibitor is complexed with either octasaccharide.

Acetylglucosaminidase↗
PubMed1984

Interaction and thermal stability of fluorescent labeled derivatives of thrombin and antithrombin III.

Derivatives of human thrombin and antithrombin III with fluorescent labels covalently attached to their carbohydrate moieties were prepared by reaction of periodate-oxidized proteins with amino derivatives of dansyl, fluorescein and pyrene. The labeled derivatives retained full biological activity, including their ability to form stable enzyme-inhibitor complexes, a reaction whose rate could be monitored by the increase in fluorescence polarization. When the dansyl-labeled derivatives were heated, they exhibited sigmoidal increases in polarization with midpoints near 50 degrees C for thrombin and 60 degrees C for antithrombin III. By contrast, a complex between antithrombin III and dansyl-thrombin showed no change in polarization up to 70 degrees C, suggesting that the individual components are more stable in the complex. These studies show that fluorescent labels attached to carbohydrate moieties of glycoproteins provide convenient probes for monitoring conformational changes and protein-protein interactions with minimum interference by the probe.

Antithrombin III↗
PubMed1984

Evaluation of critical groups required for the binding of heparin to antithrombin.

We have examined the quantitative importance of various monosaccharide residues of an octasaccharide domain of heparin that are responsible for the binding of this oligosaccharide to antithrombin. Different fragments of the octasaccharide were prepared by enzymatic digestion and the avidities of these oligosaccharides for antithrombin were determined by equilibrium dialysis. The data show that the non-reducing-end and the reducing-end tetrasaccharides contribute equally to the binding energy of the octasaccharide. The O6-sulfate group of the N-acetyl glucosamine moiety within the nonreducing-end tetrasaccharide is responsible for approximately equal to 45% of the binding energy of the octasaccharide. Neither the two non-sulfated uronic acid groups that flank this residue nor the N-sulfated glucosamine residue on the reducing end of this tetrasaccharide sequence that bears the unique O3-sulfate substituent contribute significantly to the binding energy of the octasaccharide. We suggest that the lack of sulfation of the two uronic acid moieties within the nonreducing-end tetrasaccharide may be required to permit the N-acetyl glucosamine O6-sulfate group to interact with a specific region on the antithrombin molecule. However, we cannot exclude the possibility that the O3-sulfate group plays an important role in orienting this O6-sulfate group within the nonreducing-end tetrasaccharide.

Animals↗
PubMed1981

Mechanism of precipitation of proteins by polyethylene glycols. Analysis in terms of excluded volume.

The apparent solubilities of various proteins (14,000 to 670,000 daltons) were measured in the presence of polyethylene glycols (PEGs) of different sizes. All of the solubility curves, determined by measuring the protein concentration in the supernate of centrifuged mixtures, exhibited the characteristic linear dependence of log S (g/liter) on PEG concentration (%, w/v). For human albumin in PEG-4000 at pH 4.5, this linearity extended over a 1,000-fold range of solubility, even though the appearance of the sedimented phase changed from a viscous fluid to a white amorphous solid. The slope, beta, decreased from 0.27 to 0.09 with decreasing Mr of PEG from 20,000 to 400, but was insensitive to changes in solution conditions (pH, T, salts), suggesting the absence of specific chemical interactions between protein and polymer. This conclusion was supported by the observation that concentrations of PEG up to 30% (w/v) had no significant effect on the melting temperature of ribonuclease A. Furthermore, equilibrium dialysis measurements, as well as various spectral measurements, provided no evidence for such interactions. Using a steric exclusion model (Edmond, E., and Ogston, A. G. (1968) Biochem. J. 109, 569-576) and assuming that the chemical potential of the solid phase is constant, beta can be related to interaction coefficients calculated from co-volumes using the equivalent sphere radii of PEG (r2) and protein (r3). Although good agreement was obtained for albumin in PEG-20,000, the predicted dependence of beta on r3 was greater than observed and the predicted dependence of beta on r2 was of opposite direction to that observed. However, the interaction coefficient determined from the equilibrium dialysis measurements of albumin and PEG-1000 agreed with the predicted value. Thus, the exclusion of low concentrations of PEG by albumin can be explained by a simple excluded volume model, whereas the exclusion of protein out of solution by PEG appears to be more complex.

Animals↗
PubMed1981

Thermal denaturation of antithrombin III. Stabilization by heparin and lyotropic anions.

Antithrombin III is of potential value for replacement therapy in patients with acquired or congenital deficiencies. Pasteurization of the purified inhibitor for 10 h at 60 degrees C can reduce the risk of transfusion hepatitis. Addition of appropriate stabilizers can largely prevent the loss of antithrombin activity which otherwise occurs during pasteurization. Studies of the mechanism of denaturation and stabilization have been facilitated by the use of 8-anilino-1-naphthalene sulfonate which binds weakly to the inhibitor and whose fluorescence undergoes a sigmoidal response to increasing temperature. The extent of the increase in 8-anilino-1-naphthalene sulfonate fluorescence correlates roughly with the loss of antithrombin activity and with the extent of protein aggregation as determined by high pressure liquid chromatography. The midpoint, Td, of the thermal denaturation curve increases by 13 degrees C and 19 degrees C in the presence of 0.5 M and 1.0 M sodium citrate, respectively. Phosphate, sulfate, and EDTA are also strong stabilizers while the chaotropic anions, iodide and thiocyanate are potent destabilizers. Heparin at 10 mg/ml increases Td by 7 degrees C, presumably through a direct binding mechanism; chondroitin sulfate and hyaluronic acid have no effect. Samples pasteurized for 10 h at 60 degrees C in the presence of 0.5 M and 1.0 M citrate retain essentially full activity but exhibit evidence of minor alterations in their interaction with heparin.

Anilino Naphthalenesulfonates↗
PubMed1978

The hemoglobin of the common sting-ray, Dasyatis sabina: structural and functional properties.

1. The hemoglobin of the sting-ray, Dasyatis sabina, is both polymorphic and heterogeneous; three components predominate. 2. One major component has two kinds of polypeptide chain, of which one, presumably an alpha-chain, has a blocked NH2-terminus and an arginyl COOH-terminus, whereas carboxypeptidases A and B release tyrosine and histidine from the COOH-terminus of the beta-chain. 3. The amino acid sequence of the beginning NH2-terminal segment of the beta-chain of the major component has been determined. 4. The hemoglobin of the sting-ray, Dasyatis sabina, is highly resistant to urea and does not dissociate readily into subunits. 5. Oxygen binding by the hemoglobin is not affected by organic phosphates or high concentrations of either NaCl or urea. 6. The hemoglobin does not polymerize beyond tetramers. 7. Cooperativity, as monitored by n in the Hill equation, is pH-dependent and maximal between pH 8.5 and 9.0. 8. The hemoglobin has a large Bohr effect; the oxygen affinity is 16 times higher at pH 10 than at pH 6.5.

Animals↗
PubMed1976

Tetramer-dimer dissociation in homoglobin and the Bohr effect.

The pH dependence of the apparent tetramer to dimer dissociation constant has been determined at 20 degrees for both oxy- and deoxyhemoglobins A and Kansas. These measurements were made by three different procedures: gel chromatography, sedimentation velocity, and kinetic methods in either of three buffer systems: 0.05 M cacodylate, Tris, or glycine with 1 mM EDTA and 0.1 M NaCl between pH 6.5 and 11. The tetramer-dimer dissociation constant of human oxyhemoglobin A decreases from about 3.2 X 10(-6) M at pH 6.0 to about 3.2 X 10(-8) M at pH 8.5. The slope of this line indicates that the dissociation of tetramer to dimer is accompanied by the uptake of about 0.6 protons per mol of tetramer in this region. The corresponding dissociation constant for deoxyhemoglobin in the same pH region increases apparently almost linearly from 1.0 x 10(-12) M at pH 6.5 to about 1.0 x 10(-5) M at pH 11. To dimer is associated with the release of about 1.6 protons per mol of tetramer. Comparison of these data with the known proton release accompanying the oxygenation of tetramers confirms that the pH dependence of oxygen binding by dimers must be very small. The present data predict that the overall proton release or uptake per oxygen bound by dimer should be less than 0.1. The tetramer-dimer dissociation equilibria of oxy- and deoxyhemoglobins above pH 8.5 have identical pH dependences. In this range the dissociation constant of deoxy-Hb is about one-tenth that of oxyhemoglobin. Human oxyhemoglobin Kansas is known to have an enhanced tetramer-dimer dissociation compared with that of hemoglobin A. Below pH 8.5 the tetramer-dimer dissociation constant of Hb Kansas is about 400 times greater than that of HbA in the absence of phosphate buffers. In contrast, the tetramer-dimer dissociation constants of deoxyhemoglobins A and Kansas appear to be identical. These findings are consistent with previous structural observations on these hemoglobins. The data on the tetramer-dimer dissociation of human hemoglobin were used to calculate the total free energy of binding of oxygen to the tetramer and the median oxygen pressure on the basis of fundamental linkage relations and a pH-independent estimate of the total free energy of binding oxygen to dimer. Simulated oxygen binding curves were generated with the equations of Ackers and Halvorson (Ackers, G. K., and Halvorson, H. (1974) Proc. Natl. Acad. Sci. U.S.A. 71, 4312-4316) by making two assumptions: (a) that the dimers are noncooperative and pH-independent in O2 binding and (b) that the distribution of cooperative energy in the oxygenation of tetramers is independent of pH. We have compared these simulations with experimental data obtained at low protein concentrations (30 to 124 muM heme) to show that the variation in oxygen affinity with pH can be described in terms of the subunit equilibria. We conclude that an accurate analysis of the contributions of individual oxygen binding steps to the Bohr effect cannot be made without considering the contributions of the dimers to oxygen binding...

Hemoglobins↗