Biomaterial Database

Specific binding sites on human blood platelets for plasma lipoproteins. 1982

E Koller, and F Koller, and W Doleschel

Scatchard analysis of the binding of homologous plasma low density lipoproteins (LDL) to human blood platelets shows the existence of a uniform class of saturable specific binding sites. Platelets from healthy donors bound 1470 +/- 640 molecules of LDL per platelet, the constant of association Ka = (6.2 +/- 2.2) X 10-7 l x mol-1. Binding kinetics, temperature dependence, and experiments with formaldehyde-fixed platelets showed that internalization of LDL (at least the labelled apoprotein moiety) did not occur to any considerable degree under the experimental conditions employed. Both very low density lipoproteins (VLDL) and high density lipoproteins 3 (HDL3) markedly inhibited the binding of LDL. In contrast to LDL, HDL3 bound to 3200 +/- 410 binding sites per platelet with a Ka = (9 +/- 1.7) X 10(7) l x mol-1. Additionally, the results of inhibition experiments using both LDL and HDL3 in combination gave evidence, that the sites for HDL3 binding were not identical with those for LDL binding and each inhibited binding of the other noncompetitively with reduction of the binding affinity and the number of available binding sites. VLDL bound to the platelet plasma membrane in a nonspecific-nonsaturable way. Possible significances of the presence of specific LDL receptors on the platelet plasma membrane for recognized functions of these blood elements are discussed.

UI	MeSH Term	Description	Entries
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D008077	Lipoproteins, LDL	A class of lipoproteins of small size (18-25 nm) and light (1.019-1.063 g/ml) particles with a core composed mainly of CHOLESTEROL ESTERS and smaller amounts of TRIGLYCERIDES. The surface monolayer consists mostly of PHOSPHOLIPIDS, a single copy of APOLIPOPROTEIN B-100, and free cholesterol molecules. The main LDL function is to transport cholesterol and cholesterol esters to extrahepatic tissues.	Low-Density Lipoprotein,Low-Density Lipoproteins,beta-Lipoprotein,beta-Lipoproteins,LDL(1),LDL(2),LDL-1,LDL-2,LDL1,LDL2,Low-Density Lipoprotein 1,Low-Density Lipoprotein 2,LDL Lipoproteins,Lipoprotein, Low-Density,Lipoproteins, Low-Density,Low Density Lipoprotein,Low Density Lipoprotein 1,Low Density Lipoprotein 2,Low Density Lipoproteins,beta Lipoprotein,beta Lipoproteins
D011956	Receptors, Cell Surface	Cell surface proteins that bind signalling molecules external to the cell with high affinity and convert this extracellular event into one or more intracellular signals that alter the behavior of the target cell (From Alberts, Molecular Biology of the Cell, 2nd ed, pp693-5). Cell surface receptors, unlike enzymes, do not chemically alter their ligands.	Cell Surface Receptor,Cell Surface Receptors,Hormone Receptors, Cell Surface,Receptors, Endogenous Substances,Cell Surface Hormone Receptors,Endogenous Substances Receptors,Receptor, Cell Surface,Surface Receptor, Cell
D011973	Receptors, LDL	Receptors on the plasma membrane of nonhepatic cells that specifically bind LDL. The receptors are localized in specialized regions called coated pits. Hypercholesteremia is caused by an allelic genetic defect of three types: 1, receptors do not bind to LDL; 2, there is reduced binding of LDL; and 3, there is normal binding but no internalization of LDL. In consequence, entry of cholesterol esters into the cell is impaired and the intracellular feedback by cholesterol on 3-hydroxy-3-methylglutaryl CoA reductase is lacking.	LDL Receptors,Lipoprotein LDL Receptors,Receptors, Low Density Lipoprotein,LDL Receptor,LDL Receptors, Lipoprotein,Low Density Lipoprotein Receptor,Low Density Lipoprotein Receptors,Receptors, Lipoprotein, LDL,Receptor, LDL,Receptors, Lipoprotein LDL
D001792	Blood Platelets	Non-nucleated disk-shaped cells formed in the megakaryocyte and found in the blood of all mammals. They are mainly involved in blood coagulation.	Platelets,Thrombocytes,Blood Platelet,Platelet,Platelet, Blood,Platelets, Blood,Thrombocyte
D002462	Cell Membrane	The lipid- and protein-containing, selectively permeable membrane that surrounds the cytoplasm in prokaryotic and eukaryotic cells.	Plasma Membrane,Cytoplasmic Membrane,Cell Membranes,Cytoplasmic Membranes,Membrane, Cell,Membrane, Cytoplasmic,Membrane, Plasma,Membranes, Cell,Membranes, Cytoplasmic,Membranes, Plasma,Plasma Membranes
D006801	Humans	Members of the species Homo sapiens.	Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D001667	Binding, Competitive	The interaction of two or more substrates or ligands with the same binding site. The displacement of one by the other is used in quantitative and selective affinity measurements.	Competitive Binding