Platelet Factor 4, Human (PF4)

Platelet factor-4 (PF-4) is a low molecular weight, heparin-binding protein which is secreted from agonist-activated platelets. PF-4 is localized within the platelet a-granule where its concentration ranges from 11.2-12.4ug per 109 platelets making it, on a molar basis, one of the most abundant proteins in the platelet. Since the relative concentration of PF-4 in platelets exceeds that of plasma by 280,000-fold, PF-4 levels in plasma have been utilized as a measure of platelet activation in vivo. PF-4 is secreted from platelets in complex with a high molecular weight, proteoglycan, carrier protein. Sedimentation equilibrium experiments have shown that in the absence of its proteoglycan carrier, the molecular weight of PF-4 is 27,000-29,000. Subsequent amino acid sequencing of PF-4 revealed a molecular weight of 7,800 indicating that native PF-4 is a homotetramer. Functionally, PF-4 neutralizes the anticoagulant activity of heparin in plasma. The heparin binding site within PF-4 is presumably located within the lysine-rich, COOH-terminal region of the molecule. Since soluble heparin is a therapeutic agent, the physiological significance of the anti-heparin activity of PF-4 is not known. However, by interacting with cell surface expressed heparin-like glycosaminoglycans on endothelial cells, PF-4 may exert its procoagulant effect. PF-4 binding to cell surface glycosaminoglycans may also be a mechanism through which PF-4 stimulates the release of histamine from basophils. The chemotactic activity of PF-4 toward neutrophils and monocytes has also been localized to the COOH-terminal, presumed heparin-binding domain of PF-4. While PF-4 is primarily a secreted protein, PF-4 binding sites on the platelet surface have been identified which may be important for platelet aggregation.\n\nSource:\nHuman pF-4, from supernatant of thrombin-activated platelets.\n\nMolecular Weight:\n29kD \n\nIsoelectric Point: 7.6\n\nSpecific activity: \n~170 Units/mg \n\nUnit Definition:\n1 unit will neutralize 1 IU of heparin in 1ml of normal plasma\n\nStorage and Stability:\nAliquot to avoid repeated freezing and thawing and freeze at -70 degrees C. For maximum recovery of product, centrifuge the original vial after thawing and prior to removing the cap. Aliquots are stable for at least 6 months.

Prices direct from United States Biological

Quick response times

Exclusive Biosave savings/discounts