The cystoskeleton of unstimulated blood platelets: Structure and composition of the isolated marginal microtubular band

Detergent-insoluble, marginal microtubular band (MB) cytoskeletons were isolated from unstimulated blood platelets after pretreatment with glycerol or with Taxol. MB cytoskeletons retained the shape of intact platelets and behaved in suspension as coherent structural units. The major structural component was a continuous coil of long microtubule(s), often with granular/amorphous material present in the centre; few typical actin filaments were observed. The coiled microtubules often had an amorphous surface coating, but no discrete inter-microtubule bridges were seen. Tubulin and actin (identified by immunochemical staining) were major polypeptides. None of the minor (greater than 10) polypeptide components comigrated with high molecular weight microtubule-associated proteins in brain tubulin. A novel polypeptide, resolved by two-dimensional electrophoresis and designated IEF-51K, was present in MB cytoskeletons in amounts approximately equivalent to each of the tubulin polypeptides. Evidence suggests that IEF-51K is a distinct, previously undescribed component of the platelet cytoskeletal system.