No abstract

Washed human platelets bound radioiodinated low density lipoprotein ( 125 I-LDL) to a class of saturable binding sites; they numbered 1,348±126 per platelet, and the dissociation constant (K D ) was 50.7±9 nM. I25I-LDL binding to platelets was reversible, and apparent equilibrium was attained within 25 minutes at 22°C and was characterized by forward and reverse rate constants of 1.47xlO4 Xsec"'xM" 1 and 8xlO~4xsec~' xM" 1 , respectively. Such binding was largely unaltered by temperature, divalent ions, and chelating agents. In addition, neither did receptor regulation (up or down) occur when platelets were loaded with cholesterol, nor did prostaglandin E, (PGE,) increase the binding of 12S I-LDL to platelets. On the other hand, the specificity of LDL binding was not typical of the LDL receptor of nucleated cells. Lipoproteins competed for the occupancy of LDL binding sites in platelets with the following order of potency: very low density >> intermediate density > high density subfraction 2. High density lipoprotein subfraction 3, heparin, and PGE, had no effect on this binding.

No abstract