Evidence for serotonin binding in vitro by platelet factor 4 and beta-thromboglobulin.

Evidence is presented for in vitro high affinity binding of serotonin (5-HT) by beta-thromboglobulin (beta TG) and platelet factor 4 (PF4) from human blood. Results include: 1) identification by radioimmunoassay of PF4 in specifically bound material obtained by 5-HT affinity chromatography of human platelet extracts; 2) binding of 72% and 6% of radiolabelled PF4 on 5-HT and control affinity columns, respectively; and 3) binding of approximately 8 moles of 5-HT per mole of purified beta TG in the presence of ferrous ion and heparin in ultrafiltration studies, with Scatchard analysis indicating a dissociation constant of about 4 X 10(-8) M.