Purification and properties of porcine platelet aggregating factor

Porcine platelet aggregating factor was purified from porcine plasma by a rapid batch procedure which included polyethylene glycol precipitation and adsorption on calcium citrate. The aggregating factor was separated from antihemophilic factor by gel chromatography in the presence of 1 M MgCl2. It appeared homogenous when examined by immuno- or SDS-gel electrophoresis. The molecular weight was estimated to be 10 million by exclusion chromatography. After reduction, subunit molecular weight, by sodium dodecyl sulfate (SDS)-gel electrophoresis, was 225 000. Amino acid and carbohydrate composition were similar to those reported for the bovine material. The porcine platelet aggregating factor was found to have no free sulfhydryl groups or exposed disulfide bonds. Binding of formalin-fixed washed human platelets to the aggregating factor linked to Sepharose was inhibited in 0.5 M NaCl or 2.7 M urea and reversed by the presence of free aggregating factor in a concentration-dependent manner. Ristocetin had little or no discernible effect on binding.