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Biomedical subjects

L Lorand

Publications and source records attributed to L Lorand.

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

Autoimmune antibody (IgG Kansas) against the fibrin stabilizing factor (factor XIII) system.

Serum from a patient who died from massive hemorrhage within 4 months after onset of an acquired bleeding disorder at age 85 contained a potent inhibitor of fibrin stabilization. Other parameters of coagulation and fibrinolysis and his bleeding time were within normal limits. The inhibitor was shown to be an IgG with kappa light chains (IgG Kansas); its specific target was the factor XIII system itself. Although IgG Kansas combined with the virgin [ab] form of the zymogen, it did not block the thrombin-catalyzed conversion to [a'b]. However, IgG Kansas prevented the subsequent Ca2+-mediated activation of [a'b] to a + b, where a denotes the catalytically competent factor XIIIa species. IgG Kansas, in contrast to a previously studied autoimmune antibody from a similar bleeding disorder (IgG Warsaw), could also inhibit the transamidating activity of the preactivated a enzyme.

Aged↗
PubMed1988

Fibronectin as a carrier for the transglutaminase from human erythrocytes.

Nondenaturing electrophoresis was used to demonstrate that, immediately upon exposure to plasma, the transglutaminase (protein-glutamine:amine gamma-glutamyltransferase, EC 2.3.2.13) from erythrocytes undergoes a significant shift in mobility. The plasma effect shows saturable characteristics and depends entirely on the presence of fibronectin in plasma, indicative of complex formation between this protein and transglutaminase. The results suggest a specific carrier function for fibronectin that might be of physiological importance in determining the fate of a tissue transglutaminase accidentally discharged into plasma.

Biological Transport↗
PubMed1987

Catalytic competence of human alpha- and gamma-thrombin in the activation of fibrinogen and factor XIII.

Steady-state kinetic parameters were compared for the action of alpha- and gamma-thrombin on the physiologically important thrombin substrates fibrinogen and factor XIII at 37 degrees C, pH 7.4, and 0.14 M NaCl. gamma-Thrombin, an alpha-thrombin derivative proteolytically cleaved at R-B73 and K-B154, was observed to catalyze the release of fibrinopeptide A (FPA) from fibrinogen with a specificity constant (kcat/Km) of 5 X 10(3) M-1 s-1. This value was approximately 2400-fold lower than the specificity constant for the corresponding alpha-thrombin-catalyzed reaction. The low specificity constant was attributed to an increase in Km and a decrease in kcat for gamma-thrombin-catalyzed release of FPA from fibrinogen. Conversion of alpha-thrombin to gamma-thrombin also resulted in an approximately 800-fold reduction in the specificity constant for thrombin-catalyzed release of fibrinopeptide B (FPB) from fibrin I, as well as a loss in discriminatory power. Whereas alpha-thrombin preferentially released FPA from intact fibrinogen, gamma-thrombin released FPA and FPB from intact fibrinogen at similar rates. In contrast to the large difference in specificity constants observed for alpha- and gamma-thrombin catalysis with fibrin(ogen) as substrate, the specificity constant (2.6 X 10(4) M-1 s-1) observed for gamma-thrombin-catalyzed release of activation peptide from factor XIII was only 5-fold lower than the corresponding value for the alpha-thrombin-catalyzed reaction. Additionally, the promotion of factor XIII activation by fibrin characteristic of the alpha-thrombin-catalyzed reaction did not occur in the gamma-thrombin-catalyzed reaction.(ABSTRACT TRUNCATED AT 250 WORDS)

Enzyme Activation↗
PubMed1987

Cross-linked polymers in the red cell membranes of a patient with Hb-Koln disease.

Membranes isolated from the red cells of a Hb-Koln patient were shown to contain appreciable amounts of N epsilon-(gamma-glutamyl)lysine, the characteristic product of the post-translational cross-linking of proteins by transglutaminase. Such an apparently irreversible fusion of membrane proteins may contribute to the membrane defect in Hb-Koln disease.

Adult↗
PubMed1987

Acceptor-donor relationships in the transglutaminase-mediated cross-linking of lens beta-crystallin subunits.

Following the isolation of the N epsilon-(gamma-glutamyl)lysine-containing polymers from human cataracts, our efforts were directed to induce such cross-links experimentally in rabbit lens, and evidence was obtained for the selective reactivities of certain beta-crystallin subunits in this transglutaminase-catalyzed event. In the present work, we examined the enzymatic cross-linking of purified crystallins individually (alpha, beta H, beta L, and gamma) and in combinations, with particular emphasis on forming the approximately 55K dimer. This species was the primary product in the cross-linking of beta H-crystallins; beta L also reacted with transglutaminase. Neither alpha- nor gamma-crystallins formed appreciable amounts of cross-linked structures with transglutaminase. Dansylcadaverine, known to compete against the reactive lysines of proteins in forming N epsilon-(gamma-glutamyl)lysine cross-bridges, was shown to inhibit the generation of dimeric and higher ordered oligomers from beta H and beta L. The fluorescent amine specifically labeled only two subunits in beta H (approximately 29-30K and approximately 26K) and one in beta L (approximately 26K), identifying these substrates as possessing transglutaminase-reactive endo-gamma-glutaminyl residues. An antiserum to bovine beta Bp recognized the approximately 23K subunit of rabbit beta-crystallins and also the approximately 55K dimer, suggesting that the approximately 23K protein participates as a lysine donor in generating the cross-linked dimer with transglutaminase. Inasmuch as the same antiserum reacts with an approximately 50K material reported to appear in increasing amounts with age in human lens, the results lend added support to the physiological significance of transglutaminase in the aging of lens.

Animals↗
PubMed1987

Inhibition of protein cross-linking in Ca2+-enriched human erythrocytes and activated platelets.

Treatment of human erythrocytes with Ca2+, in the presence of ionophore A23187, causes the formation of high molecular weight (greater than 10(6)) membrane protein polymers. This phenomenon, known to involve cross-linking of essentially all of the band 4.1 and 2.1 (ankyrin) proteins, as well as some spectrin, band 3, and hemoglobin molecules, could be prevented by preincubating the cells with a noncompetitive inhibitor of intrinsic transglutaminase, 2-[3-(diallylamino)propionyl]benzothiophene, at concentrations of about (3-6) X 10(-4) M. The compound also eliminated the proteolytic breakdown of the two major transmembrane proteins band 3 and glycophorin, which would otherwise occur during the Ca2+ loading of fresh human red cells. In addition, the inhibitor effectively blocked the formation of a cross-linked protein polymer in thrombin-activated human platelets.

Blood Platelets↗
PubMed1987

Isolation of a polymorphic genomic clone from chromosome 7. Physical and genetic linkage studies to markers around the cystic fibrosis locus.

A peptide prepared from purified factor 13B (F13B) was sequenced, and a single, long oligonucleotide corresponding to its cognate DNA sequence was constructed and used to screen a chromosome 7 specific genomic library. The positive clone isolated, designated pKV13, was only related to F13B at the oligonucleotide region, but has proved to be a valuable chromosome 7 marker. pKV13 maps to 7pter-q22 in hybrid cell lines, and is present in a chromosome-mediated gene transfer (CMGT) cell line that also contains met and other 7q probes. pKV13 defines a common MspI restriction fragment length polymorphism (RFLP), and is genetically linked to two markers on the long arm of chromosome 7, B79a and COLIA2, both themselves linked to the cystic fibrosis locus. Multipoint linkage analysis demonstrates that KV13 maps centromeric to both B79a and COLIA2. pKV13 has been used to demonstrate the existence of rearrangements within CMGT hybrids, and will also prove valuable in multipoint linkage studies of other 7q markers. Finally, pKV13 provides a new polymorphic locus for the characterisation of 7q deletions in myeloid disorders such as myelodysplastic syndrome.

Amino Acid Sequence↗
PubMed1987

Inhibition of beta-crystallin cross-linking in the Ca2+-treated lens.

beta-Crystallin dimers of approximately 55,000 weight are among the early products of protein cross-linking in Ca2+-treated rabbit lens, caused by the activation of intrinsic transglutaminase; formation of the cross-linked species can be blocked by 75 mM histamine (Lorand et al, Biochemistry, 24:1525-1531, 1985). As an extension of this work, we initiated a search for more specific inhibitors of cross-linking in this system. Of the compounds tested so far, hydroxylamine, methoxyamine, bisaminoxypropane and aminoacetonitrile were particularly effective, inhibiting the generation of the cross-linked dimer in the 5 to 10 mM concentration range during a 4 hr treatment of the lens with Ca2+-ions.

Animals↗
PubMed1985

Regulation of formation of factor XIIIa by its fibrin substrates.

Thrombin-catalyzed release of activation peptide (AP) from plasma factor XIII was studied to characterize the regulation of this initial step in the activation of factor XIII zymogen (fibrin-stabilizing factor). High-performance liquid chromatography was used to monitor the kinetics of release of AP. Non-cross-linked polymeric fibrins I and II (polymerized des-A- and des-A,B-fibrinogens), physiological substrates of factor XIIIa, were shown to be potent promoters of thrombin-catalyzed release of activation peptide from factor XIII. These promoters are proposed to act by complexing factor XIII and reducing the apparent Km for thrombin-catalyzed release of AP. Since thrombin-catalyzed release of AP is inefficient in the absence of polymerized fibrin, this mode of regulation should minimize formation of factor XIIIa prior to the formation of its fibrin substrates. The promoting activity of polymeric fibrin was rapidly lost when catalytically competent factor XIIIa was allowed to form. This observation suggested the possibility that factor XIIIa catalyzed cross-linking of fibrin inactivates fibrin as a promoter for the thrombin-catalyzed release of AP from factor XIII. Consistent with this view, the thiol reagent S-methyl methanethiosulfonate inactivated factor XIIIa, blocked cross-linking of fibrin, and protected against loss of its promoter activity. This mode of feedback regulation of the activation process by catalytically active factor XIIIa may serve to ensure against continued generation of factor XIIIa after its fibrin substrates have been cross-linked.

Calcium↗
PubMed1985

Formation of a 55 000-weight cross-linked beta crystallin dimer in the Ca2+-treated lens. A model for cataract.

Incubation of lens in Ca2+-containing media, considered by several investigators to be a useful model of cataract formation, gave rise to significant alterations in the covalent structures of various proteins. In rabbit lens, when sodium dodecyl sulfate-polyacrylamide gel electrophoresis was used after reduction of disulfides in urea, the most readily observable changes were (i) disappearance of 210K, 95K, and 60K proteins, (ii) modifications of alpha crystallin subunits, (iii) alterations of beta H crystallins, and (iv) de novo production of 55K and higher molecular weight polymers. The addition of leupeptin inhibited the disappearances of 210K, 95K, and 60K proteins and the alteration of alpha crystallins, suggesting that all these were caused by a Ca2+-activated protease. The proteolytically sensitive 60K species was identified as vimentin, a component of intermediate filaments. Formation of the 55K material and of higher molecular weight polymers during Ca2+ treatment of the lens could be prevented by histamine, a compound known to inhibit the transglutaminase-mediated cross-linking of proteins by epsilon-(gamma-glutamyl)lysine peptide bonds in other biological systems. It could also be shown by immunoblotting that an antibody raised against the 55K material reacted selectively with beta crystallins of normal lens. This indicates that the 55K product is in all likelihood an essential intermediate toward higher polymers and that the 55K product is a cross-linked dimer of certain polypeptides of beta crystallin.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Altered response of stored red cells to Ca2+ stress.

Short-term Ca2+ loading of erythrocytes was used as a test for probing membrane protein susceptibilities toward intrinsic enzymes in cells from fresh and from stored blood. The proteolytic response, affecting mainly glycophorin and band 3, could be elicited only in fresh cells, whereas the transglutaminase-mediated cross-linking reaction was evident both in fresh and stored cells. Loss of the proteolytic response might be an important sign of erythrocyte damage from blood bank storage.

Blood Preservation↗
PubMed1984

Activation of transglutaminase during embryonic development.

Incorporation of [3H]putrescine into proteins was shown to increase markedly in sea urchin eggs upon fertilization. Emetine, an inhibitor of protein synthesis, had no effect on the rate of protein labeling. However, the reaction could be prevented by the addition of 2-[3-(diallylamino)-propionyl]benzothiophene, a noncompetitive inhibitor of transglutaminase, and also by dansylcadaverine, which is a substrate for transglutaminase. The inert N alpha-dimethyl analogue of dansylcadaverine had no influence. Considering the complexity of the incorporation of the [3H]putrescine tracer in this system, it was deemed essential to prove by rigorous analytical methods that the reaction was, indeed, consistent with a transglutaminase mechanism. gamma-Glutamyl[3H]putrescine could be recovered in 80-90% yield from the proteolytic digest of proteins from the 20-min fertilized cell. Another sign of the in vivo activity of transglutaminase was the isolation of substantial amounts of epsilon-(gamma-glutamyl)lysine from proteins of sea urchin embryo, yielding a frequency value for this cross-link as high as 1 mol/400 000 g of protein in the 32-cell-stage material.

Acyltransferases↗
PubMed1984

Transglutaminases.

This paper is intended as a background to the topic of transglutaminases, while focusing on current ideas regarding the biological roles of these enzymes. Specifically, the following topics are discussed: geometry of forming gamma-glutamyl-epsilon-lysine cross-linked structures; energetic considerations; the gamma-glutamyl-epsilon-lysine cross-link; amine incorporation assays; artefactual incorporation of amines in cells and tissue homogenates; synthetic substrate systems; regulation of transglutaminase activities; strategies for probing transglutaminase-mediated events in biological systems; the blood clotting paradigm; transglutaminase and cell aging: the Ca2+-enriched human erythrocyte; transglutaminase and cell activation: the thrombin-stimulated human platelet and the fertilized sea urchin egg.

Acyltransferases↗