THE PRESENCE OF A COVALENTLY CROSS-LINKED MATRIX IN HUMAN PLATELETS

Exhaustive extraction of human platelets with 6 M guanidine-HCl, and 5% beta-mercaptoethanol, followed by 5% SDS resulted in a sedimentable material which showed fibrous structure by transmission electron microscopy. When platelets treated with 8 M urea, 50 mM DTT and 2% SDS were applied on a 3% solubilizable acrylamide gel a high molecular weight material could be also isolated which was highly crosslinked by epsilon(gamma-glutamyl)lysine bonds. Its amino acid composition was Asp 110, Glu 119, Ser 55, Gly 70, Arg 33, Thr 41, Ala 112, Pro 93, Tyr 35, Val 18, Met 55, Cys 46, IIe 47, Leu 71, Phe 27, Lys 76 expressed as residue per 1000. The quantity of platelet polymer material as well as the amount of epsilon-(gamma-glutamyl)lysine bond was slightly higher in thrombin activated platelets. The insoluble matrix of resting platelets reacts with antibodies against spectrin, alpha-actinin, actin, myosin, tropomyosin. The matrix from activated platelets has shown reaction with additional antibodies including ones against blood coagulation factor XIIIa, fibrinogen, von Willebrand factor, thrombospondin, tubulin and filamin. The presence of an epsilon-(gamma-glutamyl)lysine cross-linked cell matrix in platelets is consistent with the observation of a similar structure in other cells.