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Biomedical subjects

U Lindahl

Publications and source records attributed to U Lindahl.

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

Binding of platelet factor 4 to heparin oligosaccharides.

Heparin fractions of differing Mr (7800-18 800) prepared from commercial heparin by gel filtration and affinity chromatography on immobilized anti-thrombin III had specific activities when determined by anti-Factor Xa and anti-thrombin assays that ranged from 228 to 448 units/mg. The anti-Factor Xa activity of these fractions could be readily and totally neutralized by increasing concentrations of platelet factor 4 (PF4). That these fractions bound to immobilized PF4 was indicated by the complete binding under near physiological conditions of 3H-labelled unfractionated commercial heparin. An anti-thrombin III-binding oligosaccharide preparation (containing predominantly eight to ten saccharide units), prepared by degradation of heparin with HNO2 had high (800 units/mg) anti-Factor Xa, but negligible anti-thrombin, specific activity. The anti-Factor Xa activity of this material could not be readily neutralized by PF4, and the 3H-labelled oligosaccharides did not completely bind to immobilized PF4. A heterogeneous anti-thrombin III-binding preparation containing upwards of 16 saccharides had anti-thrombin specific activity of just less than one-half the anti-Factor Xa specific activity. This material was completely bound to immobilized PF4 and was eluted with similar concentrations of NaCl to those that were required to elute unfractionated heparins from these columns. Furthermore, increasing concentrations of PF4 neutralized the anti-Factor Xa activity of this material in a manner similar to that of unfractionated heparin. It is concluded that heparin oligosaccharides require saccharide units in addition to the anti-thrombin III-binding sequence in order to fully interact with PF4.

Antithrombins↗
PubMed1983

Assay of N-acetylheparosan deacetylase with a capsular polysaccharide from Escherichia coli K5 as substrate.

A new substrate for the deacetylase which catalyzes the removal of the N-acetyl groups from N-acetylheparosan in the course of heparin biosynthesis has been prepared. The capsular polysaccharide from Escherichia coli 010:K5:H4, which is structurally identical to N-acetylheparosan, was partially N-deacetylated by hydrazinolysis and was then radioactively labeled by N-acetylation with [3H]acetic anhydride. Upon incubation of the labeled polysaccharide with microsomes from the Furth mastocytoma, [3H]acetyl groups were released, demonstrating that the bacterial polysaccharide was a substrate for the N-deacetylase. Reaction conditions were established which permitted the quantitative assay of N-deacetylase activity; a Km of 74 mg polysaccharide/liter was determined, which corresponds to 2.1 X 10(-4) M, expressed as concentration of uronic acid; Vmax was 3.4 nmol/mg protein/liter. In confirmation of previous results, it was observed (a) that the reaction was stimulated by 3'-phosphoadenylylsulfate (up to a maximum of 45% at a concentration of 0.5 mM), suggesting that N-sulfation occurred which facilitated continued action of the N-deacetylase, and (b) that NaCl and KCl inhibited the enzyme, with 50% reduction of activity at a concentration of 25 mM. In the course of this work, a simple, single-vial assay procedure was used. Released [3H]acetate was extracted from the acidified reaction mixture with a toluene- or xylene-based scintillation fluid containing 10% isoamyl alcohol and measured directly by scintillation spectrometry.

Amidohydrolases↗
PubMed1982

Enzymatic depolymerization of heparin-related polysaccharides. Substrate specificities of mouse mastocytoma and human platelet endo-beta-D-glucuronidases.

Two endo-beta-D-glucuronidases acting on heparin-related polysaccharides were investigated: a mouse mastocytoma enzyme previously implicated in the postbiosynthetic modification of the heparin proteoglycan and a human platelet-derived enzyme, capable of degrading heparan sulfate as well as heparin (with elimination of anticoagulant activity). The mastocytoma enzyme was found to depolymerize a heparin precursor polysaccharide containing both N- and O-sulfate groups to fragments somewhat smaller in molecular size than commercially available heparin. In contrast, another heparin precursor species, containing N- but no O-sulfate groups was resistant to degradation. Furthermore, incubation of the mastocytoma endoglucuronidase with a heparin octasaccharide having high affinity for antithrombin failed to cleave the beta-glucuronidic linkage in the antithrombin-binding region. Previous studies established that the platelet endoglucuronidase can degrade the exclusively N-sulfated as well as the N- and O-sulfated heparin precursor polysaccharides (Oldberg, A., Heldin, C.-H., Wasteson, A., Busch, C., and Höök, M. (1980) Biochemistry 19, 5755-5762). This enzyme has now been found to attack also the beta-glucuronidic linkage in the antithrombin-binding region of the heparin molecule. The loss of bio-affinity resulting from cleavage of this linkage in the antithrombin-binding heparin octasaccharide was utilized to construct a sensitive, specific, and simple assay method for the platelet endoglucuronidase. It is concluded that the platelet endoglucuronidase has a lower degree of substrate specificity than has the mastocytoma enzyme, in reflection of the surmised functional roles of the two enzymes.

Animals↗
PubMed1982

Studies, with a luminogenic peptide substrate, on blood coagulation factor X/Xa produced by mouse peritoneal macrophages.

The formation and secretion of coagulation Factor X/Xa by mouse peritoneal macrophages was studied with a luminogenic peptide substrate (S-2613; t-butyloxycarbonylisoleucylglutamyl-gamma-piperidylglycylarginylisoluminol). Amidolysis was quantified by measuring the light emitted during oxidation of isoluminol, released by Factor Xa. A lower detection limit of about 0.5ng of Factor Xa was established; the assay was linear with enzyme concentration up to at least 100ng/ml. Factor X was determined after treatment with the Factor X-activating component of Russell's-viper (Vipera russelli) venom. Macrophages, cultured in the absence of serum, released Factor X/Xa into the culture medium. The concentration of coagulation enzyme in the medium increased in an essentially linear fashion over a period of at least 3 days, at a rate corresponding to 6-8ng produced/24h per 10(6) cells. The ratio of Factor Xa/X+Xa varied from about 60 to 100%, showing that activation of Factor X to Xa is not prerequisite to release of the enzyme from the cells. Factor Xa activity was suppressed in the presence of warfarin [3-(alpha-acetonylbenzyl)-4-hydroxycoumarin; 12.5mug/ml of medium], but could be restored by adding vitamin K (0.1mug/ml) along with the warfarin. Cultures to which Sepharose beads containing covalently bound anti-(Factor X) antibodies had been added showed decreased amounts of free Factor X/Xa in the culture medium. The missing activity could be demonstrated by incubating the recovered conjugate with the substrate peptide S-2613. Factor Xa produced by the macrophages was efficiently inactivated by heparin in the presence of antithrombin, heparin with high affinity for antithrombin being more effective than the corresponding low-affinity species.

Animals↗
PubMed1982

Effects of heparin oligosaccharides with high affinity for antithrombin III in experimental venous thrombosis.

The in vitro and in vivo characteristics of two oligosaccharide heparin fragments have been compared to those of unfractionated mucosal heparin. A decasaccharide fragment had essentially no activity by APTT or calcium thrombin time assays in vitro, but possessed very high specific activity by anti-Factor Xa assays. When injected into rabbits at doses of up to 80 microgram/kg, this fragment was relatively ineffective in impairing stasis thrombosis despite producing high blood levels by anti-Xa assays. A 16-18 monosaccharide fragment had even higher specific activity (almost 2000 iu/mg) by chromogenic substrate anti-Xa assay, with minimal activity by APTT. When injected in vivo, this fragment gave low blood levels by APTT, very high anti-Xa levels, and was more effective in preventing thrombosis than the decasaccharide fragment. However, in comparison with unfractionated heparin, the 16-18 monosaccharide fragment was only partially effective in preventing thrombosis, despite producing much higher blood levels by anti-Xa assays. It is concluded that the high-affinity binding of a heparin fragment to antithrombin III does not by itself impair venous thrombogenesis, and that the anti-Factor Xa activity of heparin is only a partial expression of its therapeutic potential.

Animals↗
PubMed1982

Further characterization of the antithrombin-binding sequence in heparin.

An octasaccharide with high affinity for antithrombin, isolated after partial deaminative cleavage of heparin and previously found to have the following predominant structure (see formula in text) has been studied further. High-voltage, paper electrophoresis of the 3H-labelled disaccharides obtained by deamination with HNO2 (pH 1.5) followed by reduction with Na[3H]BH4 showed approximately 25% of mono-O-sulfated components, in addition to L-iduronic acid(2-O-SO3)-2,5-anhydro-D-[3H]mannitol (6-O-SO3). The monosulfated disaccharides were identified by high pressure, ion-exchange chromatography as L-iduronic acid(2-O-SO3)-2,5-anhydro-D-[3H]mannitol, L-Iduronic acid-2,5-anhydro-D-[3H]mannitol(6-O-SO3). and D-glucuronic acid-2,5-anhydro-D-[3H]-mannitol L, iduronic acid 2,5-anhydro-D-[3H]mannitol(6-O-SO3), and D-glucuronic acid-2,5-anhydro-D-[3H]-mannitol. These components originated from the reducing, terminal disaccharide residue (units 7 and 8), as indicated by selective labelling with Na[3H]-BH4. The structural variability within this region suggests that it is not part of the antithrombin-binding sequence. Neither enzymic removal of the non-sulfated L-iduronic acid unit 1 nor N-deacetylation (by hydrazinolysis) at unit 2 had any significant effect on the affinity of the octasaccharide for antithrombin. However, removal of the disaccharide corresponding to units 1 and 2, by selective deamination of the N-deacetylated octasaccharide, yielded a low-affinity hexasaccharide. In addition, a high-affinity deamination product was formed, presumably an octasaccharide containing a 6-sulfated 2-deoxy-2-C-formyl-D-pentofuranosyl unit due to ring contraction in unit 2. These results suggest that the 6-sulfate group in unit 2 may be involved in antithrombin binding. It is concluded that the antithrombin binding site in heparin is represented by the pentasaccharide sequence extending from unit 2 to unit 6 of the octasaccharide studied.

Animals↗
PubMed1981

Effect of cycloheximide, beta-D-xylosides and beta-D-galactosides on heparin biosynthesis in mouse mastocytoma.

Heparin biosynthesis has been investigated with mouse mastocytoma in vitro. Minced tumour tissue catalysed the incorporation of [35S]sulphate and [3H]glucosamine into heparin and to a smaller extent into chondroitin sulphate. Addition of cycloheximide caused an inhibition (greater than 80%) of incorporation of each labelled precursor into both polysaccharides. Addition of benzyl beta-D-xyloside relieved the inhibition of incorporation into chondroitin sulphate and restored it to more than threefold that of the control incubation. The effect of beta-D-xyloside on incorporation into heparin was less marked although a consistent small increase of incorporation into this polysaccharide was observed. beta-D-Xyloside did, however, cause a marked incorporation of 35S and 3H labels into material of low molecular weight, which appeared to comprise heparin-like fragments. It is proposed that these fragments arise through a breakdown of the usual process of heparin biosynthesis.

Animals↗
PubMed1980

Isolation and characterization of heparin from human mastocytoma tissue.

Polysaccharide was isolated from human spleen mastocytoma by proteolytic digestion, precipitation with cetylpyridinium chloride, digestion with chondroitinase ABC, and ion-exchange chromatography on DEAE-cellulose. The final product (0.7 mg per g of starting material, MW 8000) behaved like standard heparin on ion-exchange chromatography and on electrophoresis, and contained D-glucuronic acid, L-iduronic acid, D-glucosamine and sulfate in the proportions expected for heparin. Affinity chromatography on antithrombin-Sepharose separated a distinct high-affinity fraction (4-5% of the total material). Structural analysis of this fraction showed that about 10% of the D-glucosamine residues were N-acetylated, the remainder N-sulfated. The anticoagulant activity of the isolated heparin was 71 B.P. units per mg (whole-blood system), or 30 units per mg (anti-thrombin and chromogenic substrate). 205 and 10-15 units per mg (chromogenic assay) were found for high and low affinity fractions, respectively. These results demonstrate conclusively the occurrence of heparin in a human tissue.

Chromatography, Affinity↗