Polymorphism of alpha-actinin from human blood platelets. Homodimeric and heterodimeric forms.

In purified solutions of alpha-actinin from human blood platelets, three polypeptides a, b and c, of approximately 100 kDa, were observed by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. They were identified as alpha-actinin subunits on the basis of their cross-reactivity with antibodies against skeletal muscle alpha-actinin and their interaction with F-actin. After electrophoresis in the absence of sodium dodecyl sulfate, six forms were observed: aa, ab, bb, ac, bc, cc. The similarity between the one-dimensional peptide maps of a and b and the absence of b in the presence of calcium-dependent protease inhibitors indicated that b is probably derived from the a subunit. The c subunit differs from the a subunit. The results provide evidence that there are actually only two platelet alpha-actinin subunits a and c which give rise to three isoforms: two homodimers aa and cc, and one heterodimer ac.