PLATELET MEMBRANE ACTIN MAY BE PARTIALLY EMBEDDED IN LIPID BILAYER AND DISULFIDE-LINKED

When platelet membranes previously treated by 0.6M KI were reacted wit h C-14-NEM, 9 protein bands including membrane actin were labeled. If KI treated platelet membranes were first reacted with cold NEM, beta-M ercaptoethanol, and 14C-NEM sequentially only three protein bands, one of which was actin, were labeled. These results imply that some of th e tightly associated membrane actin thiol groups are free and some of them form disulfide bonds with two other labeled proteins. The candida tes that might form disulfide bonds with actin were identified by mono clonal antibody to be GpIIb and/or GpIIIa. Extraction experiments show ed that even when the disulfide bonds that link actin to membrane inte gral protein were first reduced by DTT and then extracted with 0.6M KI , membrane actin still remained tightly associated to the membrane by some other means. Membrane actin could be extracted with 1% octyl gluc oside but remained as part of a high-molecular-weight complex. From th ese results we believe that platelet membrane actin may be partially e mbedded into the bilayer of the lipid membrane and disulfide linked to membrane integral proteins. It may thus act as a nucleating center fo r the polymerization of cytosolic actin in the assembly of the cytoske leton. (C) 1998 Academic Press.