Identification of binding sites for factors IX and IXa on human platelets

Conference · Fri May 01 04:00:00 EDT 1987 · Fed. Proc., Fed. Am. Soc. Exp. Biol.; (United States)

OSTI ID:6024768

Ahmad, S S; Rawala, R; Walsh, P N

Previous studies from the authors laboratory have demonstrated that factors IX (FIX) and IXa (FIXa) bind to a common site on thrombin-activated human platelets in the presence of calcium ions. The present studies provide evidence that FIXa also binds to a site distinct from that for FIX. FIX was isolated from human plasma by immunoaffinity chromatography utilizing a murine monoclonal antibody. For binding experiments gel filtered platelets were incubated at 37/sup 0/C with either /sup 125/I-FIX or /sup 125/I-FIXa, and aliquots were centrifuged through silicone oil barriers to separate the platelets from unbound proteins. Binding of both zymogen and enzyme required the presence of calcium ions, platelet stimulation and was specific, reversible, and saturable. A linear relationship was demonstrated between platelet concentration and the amount of FIXa bound. Unlabeled FIX and FIXa competed with radiolabeled FIXa for binding sites on activated platelets. In contrast, no competition was observed with 50- to 140-fold excesses of FXI, prekallikrein or high Mr kininogen; FX and prothrombin showed slight competition. Scatchard analysis of the binding yielded significantly more binding sites for FIXa on platelets than for FIX, with similar dissociation constants of approximately 2.6 to 2.7 nM. Further studies on bound ligands suggested that FIXa binding to platelets can contribute to FX activation.

• Research Organization: Temple Univ., Philadelphia, PA
• OSTI ID: 6024768
• Report Number(s): CONF-870644-
• Conference Information: Journal Name: Fed. Proc., Fed. Am. Soc. Exp. Biol.; (United States) Journal Volume: 46:6
• Country of Publication: United States
• Language: English

Related Subjects

550201* -- Biochemistry-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
ANIMALS
ANTIBODIES
BETA DECAY RADIOISOTOPES
BIOCHEMICAL REACTION KINETICS
BIOLOGICAL MATERIALS
BLOOD
BLOOD CELLS
BLOOD PLATELETS
BODY FLUIDS
CARBOHYDRATES
CHROMATOGRAPHY
COMPARATIVE EVALUATIONS
DAYS LIVING RADIOISOTOPES
ELECTRON CAPTURE RADIOISOTOPES
GLUCOPROTEINS
INTERMEDIATE MASS NUCLEI
IODINE 125
IODINE ISOTOPES
ISOTOPE APPLICATIONS
ISOTOPES
KINETICS
LIGANDS
MAMMALS
MAN
MATERIALS
MEMBRANE PROTEINS
MICE
MONOCLONAL ANTIBODIES
NUCLEI
ODD-EVEN NUCLEI
ORGANIC COMPOUNDS
PRIMATES
PROTEINS
RADIOISOTOPES
REACTION KINETICS
RECEPTORS
RODENTS
SACCHARIDES
SEPARATION PROCESSES
TRACER TECHNIQUES
VERTEBRATES