Heparin/Platelet Factor 4 (HPF4)

Platelet factor 4 (PF4) is a platelet-derived protein capable of binding to, and thus neutralizing, the biological activities of heparin and heparan sulphate. Heparin-derived saccharides were incubated with each of the three proteins, followed by separation of free and protein-bound carbohydrate on a nitrocellulose filter. Species smaller than octasaccharides were unable to bind AT, whereas binding to FN and PF4 increased continuously throughout the series, with increasing size of the oligosaccharides. Further separation by anion-exchange chromatography showed that the PF4-binding and FN-binding octasaccharides represented essentially all components present in the initial octasaccharide fraction, the proportion of binding species increasing with charge. The AT-binding octasaccharides, on the other hand, selectively represented only a few of the total octasaccharide components, without any correlation to overall charge.