Peripheral and Integral Proteins of Human Blood Platelet Membranes. Alpha-Actinin is Not Identical to Glycoprotein III

Isolation of human platelet membranes on polylysine beads and selective solubilization of membrane proteins allowed classification of membrane-associated proteins into integral and peripheral proteins. No major integral protein was found that was not exposed on the surface. Glycoprotein Ic was the only surface-exposed protein that behaved as a peripheral protein. The localization and identification of alpha-actinin was performed with an antibody against porcine skeletal muscle alpha-actinin. Human platelet alpha-actinin had an apparent molecular weight of 100 000 and a pI of 5.7-6.3. It was membrane-associated and behaved as a peripheral protein. Immunoisolation on protein A beads, as well as the 'Western Blot' technique applied to two-dimensional gels, demonstrated that alpha-actinin is not identical to GP III as was previously suggested (Gerrard, J.M., Schollmeyer, J.V., Phillips, D.R. and White, J.G. (1979) Am. J. Pathol. 94, 509-528).