PURIFICATION AND PARTIAL CHARACTERIZATION OF A NOVEL HUMAN PLATELET-AGGREGATION FACTOR IN THE EXTRACELLULAR PRODUCTS OF STREPTOCOCCUS-MITIS, STRAIN NM-65

human blood platelet aggregation factor was purified from the extracel lular products (ECP) of Streptococcus mitis, strain Nm-65 by sequentia l chromatography on DEAE-Sepharose CL-6B, hydroxyapatite and Superdex 75 columns. The purified factor (S. mitis-derived human platelet aggre gation factor, Sm-hPAF) gave a single band with a molecular weight of 66 kDa on SDS-polyacrylamide gel electrophoresis (SDS-PAGE). Sm-hPAF s howed a peak absorption at 278 nm and an isoelectric point of around 8 .5. Chemical analyses revealed that Sm-hPAF contained no sugars and th at its first 15 amino-terminal amino acid residues were H-DEQGNRPVETEN IAR. Platelet aggregation activity of Sm-hPAF was abolished by heating at 45 degrees C for 10 min. Platelet aggregation by Sm-hPAF was accom panied by a release of prostaglandin E(2) (PGE(2)) in a dose-dependent manner: The platelet aggregation was not inhibited by either prostagl andin E(2) (PGE(1)) or Gly-Arg-Gly-Asp-Ser (GRGDS), that inhibit the p latelet aggregation induced by collagen, Twenty (77%) platelet rich-pl asma (PRP) specimens derived from 26 healthy volunteers were aggregate d by Sm-hPAF, but the remaining 6 (23%) were not reactive, A prelimina ry study suggested the presence of an inhibitory factor against Sm-hPA F in the plasma from a non-reactive donor.