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At least 19 recordsLinked to original sources
PubMed1979

Structural analysis of human platelet membrane glycoprotein I complex.

The glycoprotein I complex, consisting of two polypeptides of Mr 210,000 and 150,000, was isolated from human platelet membranes by wheat germ lectin affinity chromatography. Glycocalicin, a soluble loosely bound membrane glycoprotein of Mr 150,000 related to the glycoprotein I system, was also purified. The isolated polypeptides were radioiodinated in sodium dodecyl sulfate/polyacrylamide gels and digested with trypsin, and the labeled peptide digest was analyzed by two-dimensional high-voltage electrophoresis and thin-layer chromatography. The two polypeptides of Mr 210,000 and 150,000 in the glycoprotein I complex had essentially identical radioactive peptide maps. Glycocalicin had a completely different tryptic peptide map. These studies shed light on the molecular relationships of some of the components of the platelet membrane glycoprotein I system. The possibility is raised that the receptorlike function of the intrinsic platelet membrane glycoproteins may be related to the polymeric subunit associations of the constituent polypeptides.

Blood Platelets↗
PubMed1979

Platelet membrane glycoproteins in thrombasthenia, Bernard-Soulier syndrome, and storage pool disease.

Quantitative polyacrylamide gel electrophoresis has been carried out on patients with Bernard-Soulier syndrome, Glanzmann's thrombasthenia, and storage pool defect in order to clarify the abnormalities in their platelet membrane glycoproteins. Normal individuals had values (expressed as PAS staining units/mg of membrane protein) of 5.11 +/- 0.63 for glycoprotein 1 (Mr 150,000), 2.35 +/- 0.35 for glycoprotein II (Mr 120,000), 0.89 +/- 0.22 for glycoprotein III (Mr 100,000), and 1.34 +/- 0.64 for glycoprotein IV (Mr 85,000). Total PAS staining of these four major bands was 9.70 +/- 1.26 PAS units/mg of membane protein. Patients with Bernard-Soulier syndrome completely lacked glycocalicin and had about one half (1.90 PAS units/mg) of the glycoprotein I of normal controls. These was no significant reduction in glycoproteins II, III, and IV, but total PASstaining was reduced to 4.40 units/mg, reflecting the importance of the contribution of glycoprotein I to this parameter. Thrombasthenic platelets gave values for glycoprotein II of 0.66, which were about 25% of controls, and the values for glycoprotein III (0.34) were about 40% of controls. Patients with storage pool disease gave values within the normal range with the exception of one family which showed, in addition, small platelets and an associated lipid defect. In thic case of glycoprotein (2.71) was significantly elevated.

Blood Platelet Disorders↗
PubMed1979

Platelet membrane glycoproteins in normal dogs and dogs with hemostatic defects.

Glycoproteins solubilized from membrane-enriched fractions of platelets from dogs with TT or VWD and from normal controls were compared by SDS-PAGE. The results were similar to those for the analogous human disorders. Both normal and VWD canine platelet MPs contained three major glycoproteins as well as four smaller-molecular-weight proteins that stained for carbohydrate with the PAS reagent. In contrast, MPs from dogs with TT had a higher concentration of GP I, a varied expression of GP II, and a lower concentration of GP III. The findings re-emphasize the value of comparative studies of these models of human hemostatic defects.

Animals↗
PubMed1979

Human platelet membrane receptor for bovine von Willebrand factor (platelet aggregating factor): an integral membrane glycoprotein.

The platelet membrane receptor for bovine von Willebrand factor, platelet aggregating factor, has been reported to be a property of a soluble glycoprotein, glycocalicin, that is loosely attached to the platelet surface and represents one of the major glycoproteins of the platelet glycocalyx. The studies reported here, however, demonstrate that fractions from human platelets containing glycocalicin have no bovine von Willebrand factor receptor activity. Instead, only fractions containing platelet membranes have receptor activity. By using a nonionic detergent, Brij 99, active receptor can be solubilized from the membrane. Some quantitation of the intact or solubilized receptor activity is possible because the aggregation curves produced by mixtures of various dilutions of membranes and a constant concentration of standard normal bovine plasma are linear when plotted against the logarithm of the concentration of receptor. The dose-response curve obtained with Brij 99-solubilized membranes is not parallel to that obtained with intact membranes. Lectin-specificity studies of the bovine von Willebrand factor receptor, soluble in Brij 99, demonstrate binding to a wheat germ agglutinin-Sepharose 4B affinity gel but little or no binding to similar affinity gels of concanavalin A or Lens culinaris lectin. By using wheat germ agglutinin-Sepharose 4B as a lectin affinity column, partial purification of the receptor is possible. Stability studies of the receptor in intact membranes show essentially no loss of activity for at least 6 days when membranes are stored at 4 degrees C in buffers containing 1 mM EDTA. One freezing and thawing cycle results in minimal loss of initial activity but the receptor activity of the thawed material is less stable over time than is fresh material. Repeated freezing and thawing destroys the activity and, once lost, it can not be recovered, even with detergents.

Blood Coagulation Factors↗
PubMed1979

High resolution two-dimensional gel electrophoresis of the proteins and glycoproteins of human blood platelets and platelet membranes.

The proteins and glycoproteins of human blood platelets and platelet membranes in both the reduced and the unreduced states have been analysed by isoelectric focusing and sodium dodecyl sulphate-discontinuosus polyacrylamide gel electrophoresis in a two-dimensional technique. Gels which had been stained with periodic acid-Schiff's reagent could be counter-stained with Coomassie Brilliant Blue, simplifying the recognition of components which stain with both reagents. The major glycoproteins and some of the proteins have been identified and the characteristics of the membrance and of the whole platelet components established in this system.

Blood Platelets↗
PubMed1979

Comparison of fibrinogen association with normal and thrombasthenic platelets on exposure to ADP or chymotrypsin.

Although 125I-fibrinogen becomes associated with washed platelets from normal human subjects during ADP-induced shape change and aggregation, 125I-fibrinogen did not become associated with washed plateletes from a thrombasthenic subject during ADP-induced shape change and the platelets did not aggregate. Platelets from control and thrombasthenic subjects were treated with chymotrypsin, which is known to degrade platelet membrane glycoproteins. More 125I-fibrinogen became associated with chymotrypsin-pretreated platelets from normal subejcts than with untreated platelets, and fibrinogen caused the enzyme-treated platelets to aggregate. 125I-fibrinogen did not become associated with chymotrypsin-pretreated thromobasthenic platelets, and fibrinogen did not aggregate them. Thus, there appears to be a defect in thrombasthenic platelets that prevents the association of fibrinogen with them.

Adenosine Diphosphate↗
PubMed1979

Studies on the mechanism of ristocetin-induced platelet aggregation: binding of factor VIII to platelets.

The effect of ristocetin on the binding of [125I]factor VIII to platelets was studied. High and low affinity F.VIII binding sites exist on platelets. The high affinity sites bind 13 times more F.VIII than the low affinity sites. Ristocetin increased the binding of F.VIII to both types of binding sites by increasing the affinity of F.VIII for the platelet and increasing the total number of platelet binding sites. Chymotrypsin-treated platelets were not aggregated by ristocetin and F.VIII: these platelets have less of the major platelet membrane glycoproteins and bind much less [125I]F.VIII than do buffer-treated platelets with and without ristocetin.

Antigens↗
PubMed1979

Spontaneous platelet aggregation in cerebrovascular disease II. Further characterisation of the platelet defect.

A group of 186 patients with Transient Ischaemic Attacks (TIA) or cerebral infarction (CI) was found to demonstrate in vitro Spontaneous Platelet Aggregation (SPA) in 39% of those studied. Of the 176 normal subjects studied the incidence on in vitro SPA was found to be 5%. Further investigation of the phenomenon of SPA revealed that: 1. it is associated with ADP-hyperaggregability, i. e. the threshold concentration to induce second wave aggregation is decreased; 2. it is dependant on the increase in pH which occurs in platelet-rich plasma stirring in an aggregometer while concurrent ADP-hyperaggregability is independant of this change in pH; 3. it is associated with malondialdehyde production and the release of endogenous 5-hydroxytryptamine; and that 4. in addition Km and Vmax values for [14c]-5HT incorporation are normal; and that 5. no gross abnormalities of the platelet membrane glycoproteins were apparent although occasionally glycoprotein III was found to be increased. This study demonstrates abnormal platelet behaviour in patients with TIA and CI where the enzyme system involved in thromboxane production is sufficiently stimulated, by stirring alone, to induce aggregation of platelets and the release reaction. Acetylsalicylic acid abolishes SPA and prolongs the bleeding time with similar characteristics as has been described for normal individuals. Plasma beta-thromboglobulin levels are significantly increased in the patients studied. However, no correlation was established with the incidence of in vitro SPA.

Adenosine Diphosphate↗
PubMed1977

Comparative studies on the glycoprotein composition of mammalian platelets.

1. The membrane glycoprotein composition of the blood platelets of 13 mammalian species has been compared by SDS-polyacrylamide gel electrophoresis. 2. A basic pattern of 2-3 predominant high molecular weight glycoprotein bands was observed, however species differences in their relative rates of migration and abundance were apparent. 3. Wide species differences in the number and rate of migration of the acidic glycopeptides released by trypsin digestion of washed platelet suspensions were observed following polyacrylamide gel electrophoresis in the absence of SDS.

Animals↗
PubMed1979

Galactosyltransferase and membrane glycoprotein abnormality in human platelets from Tn-syndrome donors.

Early studies on the analysis of membranes isolated from the erythrocytes of Tn-patients by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) revealed a severe reduction in the staining capacity of glycophorin with the periodate-Schiff (PAS) reaction. A low sialic acid and galactose (Gal) content of the polyagglutinable red cells was confirmed while it was reported that the abnormal red cells of Tn-patients contained little or no UDPGal: GalNAc-beta-3-D-galactosyltransferase (T-transferase) activity. The glycoprotein (GP) abnormality in Tn-erythrocytes appeared to be due to incomplete synthesis of the alkali-labile oligosaccharide chaims of glycophorin. We now report studies on the membrane GP composition and the T-transferase activity of platelets isolated from there Tn-syndrome patients whose red cell membranes contain GP abnormalities which are typical of those found in this rare clinical condition.

Blood Group Antigens↗
PubMed2026

Inherited Platelet GPIV Deficiency: First Description of a Series of Unrelated Patients with Bleeding Diathesis.

GPIV (CD36) is a multifunctional membrane protein expressed on various cells, including platelets, where it plays a role in adhesion and activation through the interaction with its ligands, including collagen types I and III and thrombospondin 1. Inherited GPIV deficiency, historically recognized in anti-Naka alloimmunized East Asian donors, is considered asymptomatic and associated with normal platelet aggregation, although impaired adhesion under high-flow conditions has been reported. Here, we reconsider the molecular basis, epidemiology and functional consequences of GPIV deficiency and report four unrelated patients in whom heterozygous CD36 variants are associated with markedly reduced platelet GPIV expression and a clinically relevant mucocutaneous bleeding diathesis. Patients suffered lifelong bleeding symptoms despite normal light-transmission aggregometry and platelet granule content and release and displayed decreased GPIV expression. Three of them showed slightly decreased VWF. Platelet adhesion to Type I collagen was reduced at high shear. These cases suggest for the first time an association between CD36 gene variants and bleeding and underscore the importance of including GPIV in the diagnostic workup of inherited platelet disorders, particularly when conventional assays do not reveal abnormalities.

Humans↗