Summary
Actin-binding protein (ABP) is degraded into fragments of 190 and 90 kDa by calpain.
A monoclonal antibody (MAb TI10) against the 90 kDa fragment of ABP coprecipitated
with the glycoprotein lb (GP lb) peak observed on crossed immunoelectrophoresis of
Triton X-100 extracts of platelets prepared without calpain inhibitors. MAb PM6/317
against the 190 kDa fragment was not coprecipitated with the GP lb peak under such
conditions. The 90 kDa fragment was adsorbed on protein A agarose from extracts that
had been preincubated with antibodies to GP lb. This supports the idea that the GP
Ib-ABP interaction resides in the 90 kDa region of ABP. GP lb was sedimented with
the Triton-insoluble actin filaments in trace amounts only, and only after high speed
centrifugation (100,000 × g, 3 h). Both the 190 kDa and the 90 kDa fragments of ABP were sedimented with the
Triton-insoluble actin filaments.
