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
S Niewiarowski, DA Walz, P James, B Rucinski and F Kueppers
Low-affinity platelet factor 4 and beta-thromboglobulin are low molecular
weight platelet secretory proteins that have common antigenic determinants.
Four amino acids (Asn-Leu-Ala-Lys) at the amino terminus of
beta-thromboglobulin are deleted, but the remaining sequences of the two
peptides appear to be identical. Low-affinity platelet factor 4 and
beta-thromboglobulin 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. It has been determined that the supernate processes immediately
after platelet aggregation induced by ionophore A23187 or thrombin contains
approximately 80% low-affinity platelet factor 4, 8% beta-thromboglobulin,
and 12% highly cationic immunoreactive material (platelet basic protein).
Experimental evidence suggests that low- affinity platelet factor 4 is
originally secreted by platelets and then converted to beta-thromboglobulin
by a platelet-derived, heat-labile protease that is inhibited by
phenylmethylsulfonyl fluoride.
Volume 55,
Issue 3,
pp. 453-456,
03/01/1980
Copyright © 1980 by The American Society of Hematology
