IDENTIFICATION AND SEPARATION OF SECRETED PLATELET PROTEINS BY ISOELECTRIC-FOCUSING - EVIDENCE THAT LOW-AFFINITY PLATELET FACTOR-4 IS CONVERTED TO BETA-THROMBOGLOBULIN BY LIMITED PROTEOLYSIS

  • 1 January 1980
    • journal article
    • research article
    • Vol. 55  (3) , 453-456
Abstract
Low-affinity platelet factor 4 and .beta.-thromboglobulin [.beta.-TG] are low MW platelet secretory proteins that have common antigenic determinants. Four amino acids (Asn-Leu-Ala-Lys) at the amino terminus of .beta.-TG are deleted, but the remaining sequences of the 2 peptides appear to be identical. Low-affinity platelet factor 4 and .beta.-TG have respective isoelectric points at pH 8.0 and at pH 7.0. Identification, quantitation and separation of both proteins was achieved by a method combining preparative isoelectric focusing and specific radioimmunoassay with anti-low-affinity platelet factor 4 antibody. The supernate processed immediately after platelet aggregation induced by ionophore A23187 or thrombin contains approximately 80% low-affinity platelet factor 4, 8% .beta.-TG and 12% highly cationic immunoreactive material (platelet basic protein). Low-affinity platelet factor 4 is apparently originally secreted by [human] platelets and then converted to .beta.-TG by a platelet-derived, heat-labile protease that is inhibited by phenylmethylsulfonyl fluoride.